and the Necessity of Belief in it
Throughout the history of Islam, different sects have debated among themselves the question of whether inerrancy is necessary in prophets and Imams or not.
The Shi'ah are unanimously agreed on the inerrancy ('ismah) of the Imams, and they regard only the one who possesses this fundamental quality as fit for the office of Imamate, given the sensitive and portentous nature of the office. There is always the danger that a leader burdened with responsibility for the manifold concerns of the ummah may knowingly or unknowingly veer in the direction of error, in which case the honor and values of the ummah will be at risk, with undesirable consequences for Islamic society as a whole.
Insistence upon inerrancy as a condition for leadership is a hallmark of the Shi'ah and a proof of the maturity of their religious thinking and comprehensive grasp of Islam, for with great care and alertness they have identified who the leader should be and designated inerrancy and extensive knowledge as two of his inseparable qualities. His inerrancy and immunity from sin are the result of his piety and self-discipline, and his knowledge is the result of divine grace and generosity, bestowed upon him from God's limitless ocean of wisdom. These two qualities are to be found in combination only in the Imams of the Prophet's Household, peace and blessings be upon him and his family. The Sunnis accept anyone as caliph or Imam, without any precondition, and they do not insist on inerrancy and immunity from sin.
Inerrancy is an inner faculty of self-restraint, springing up from the great source of faith, piety, and insight; it insures man against all kinds of sin and moral corruption. This powerful inner attribute, derived as it is from vision of the suprasensible world and the very essence of all creation, is so effective that it prevents man from embarking on any kind of sin or rebellion, whether small of great, open or hidden.
When we say that the factors leading to rebellion and sin have no effect on such a person, we do not mean that in accordance with divine with and decree an overwhelming force prevents him from being attracted to sin, so that the capacity to sin and disobey is removed from him. It is rather that the possessor of inerrancy, while having freedom to choose and to act, is prevented by his awareness of the majesty and constant presence of God from approaching the sphere of sin. He has had such success in establishing the dominion of piety over his soul that he cannot even conceive of sin in the purified sanctuary of his mind, so that the possibility of his actually committing a sin is reduced to zero.
Generally speaking, the commission of any undesirable act is the result of not knowing how ugly the act is and how harmful its consequences are. Even if one is aware to a certain extent of the ugliness of the act and his faith seeks to warn him and alert him to the danger, he is overpowered by his desires and loses all self-control, and is drawn to impurity and sin. It is only attention to the damaging consequences of one's deeds, the restraining force of piety, and a powerful sense of obedience toward divine law, that create a certain immunity in man; there will then be no need for any other means of restraint and control. Muhammad b. Abi 'Umayr says: "I asked Hisham, the celebrated pupil of Imam Ja'far al-Sadiq, peace be upon him, whether the Imam possessed the quality of inerrancy. He answered that he did, and I then asked him to explain inerrancy to me.
"He said: 'Several things hie at the origin of rebellion and sin - greed, envy, lust, anger, and so forth and not one of these can penetrate the being of the Imam. How might he be greedy, considering that he has everything at his disposal, including even the treasury of the Muslims? How might he be envious, for only he who is aware of a station higher than his own can be envious, and no station higher than the Imamate can be conceived? As for anger, it is impossible that the Imam be angered by any worldly concern, for God has entrusted to him the implementation of His laws. But in connection with anything touching on the hereafter, anger in not at all undesirable. The Imam will never fall prey to lust, for he is well aware that the pleasures and desirable things of this world are transitory and valueless when compared to the reward that God shall bestow on His worshippers on the Day of Resurrection." 
People will submit fully to the requirements of religious duty in response to the summons of their leader and unquestioningly accept his commands and instructions when they regard all his orders as being the command of God, without having doubt on the matter. If someone not be thoroughly immune to sin and error, can complete trust be placed in his words or his orders be obeyed with devotion?
The effect of inerrancy is such that it protects man from deception by the allurements of this world power and position, wealth and possessions and enables him to remain steadfast in the face of all types of distraction.
If it is not possible to trust the leader fully, the mission of religion, which is to enable man to attain perfection, will necessarily remain unfulfilled, for the credal structure of the religion will be distorted by inevitable suspicions that the commands and edicts of the leader are not based on revelation and the authentic principles of Islam.
In addition, possession of the attribute of inerrancy cannot be restricted to the period in which the leader of the Muslims actually exercises the office of Imam. Throughout his life, including the period before assuming the Imamate, his heart must have been free of all darkness and his person of all sin. In addition to the fact that sinning entails a loss of human dignity, people will always suspect of continuing sinfulness and pollution one whom they know to have erred in the past, however slightly. This suspicion will in turn rob the leadership of such a person of all legitimacy. He will no longer be regarded as an exemplar of piety and purity, as one endowed with unique virtues.
The bitter memory of a life spent partially in sin and corruption can never be erased, and it will always serve as a pretext for his opponents. They will have a powerful and credible tool for attacking him and destroying his reputation and base of popular support. He will be unable to defend his honor or answer his critics convincingly.
If we examine the life of the Immaculate Imams, peace be upon them, we will see that the groups opposed to them, for all their impudence and shamelessness, never resorted to accusations of corruption in order to destroy their reputation. If there had been the slightest grounds for making such an accusation, the enemies of the Imams would never have remained silent, and the people in general would have entertained doubt concerning the Imams' pronouncements on matters relating to revelation and God's law. We read in the story of Musa, peace be upon him, that the Fir'awn (Pharaoh), that cruel tyrant, unhesitatingly pointed the finger of accusation at Musa when he confronted him, saying:
"Are you not that child that grew up under our tutelage and spent many years with us ? Who then committed murder and rebelled against our divinity?" Musa answered: "Yes, indeed I killed someone, but not deliberately; my intention was to save an oppressed person, and the result was and accidental killing. I then fled out of fear of you until my Lord taught me knowledge and wisdom and appointed me as one of His prophets." (26:16-19)
The first and most essential condition for the office of Imamate is, then, inward purity and profound piety, divinely accorded protection from sin, the possession of a lustrous heart both before and after appointment to the rank of leader and Imam.
It is true that everyone is exposed to the possibility of error, for the simple reason that whatever knowledge and information he has consists of a series of concepts and images acquired by means of the senses and other ontological faculties, none of which are infallible.
However, the Imam observes the innermost nature of the world, including its suprasensible aspect, by means of the eye of the heart, and this grants him access to a whole treasure house of true and certain knowledge. His perception of reality is not dependent on his senses and is for this reason immune against error. Fallibility arises only when a person wishes to apply his mental concepts to the world of external reality; it does not exist in the case of the Imam who has a direct and unmediated perception of reality and is inwardly connected with the essence of all being,
The comprehensive infallibility and inerrancy of the Imam, manifested in his speech, his acts, and his thoughts, results from his privileged knowledge of the realm of the unseen. No one can comprehend the totality of reality by recourse to external and conventional means, and perceive the true nature of things as they are; it is only divinely bestowed knowledge, a mode of comprehension derived from the world of the unseen, that can guide man infallibly to a knowledge of the reality of all things.
Piety expressing itself in deeds is far more effective than verbal exhortation in bringing about the moral education of men and advancing them on the path of spiritual growth. If the one who assumes the task of the spiritual guidance of the people is lacking himself in spiritual virtue and no sign of moral purity or practical piety can be discerned in him, he will be totally unable to fashion upright and exalted human beings, to exercise any positive role in their development, or to guide them toward the general goals inculcated by religion.
It may appear that the Qur'an has attributed sins to some of the prophets. However, the sin must be carefully examined in each case to gain a proper understanding of the matter. The essence of true sin is to rebel against God, to disobey His commands, to plunge into the whirlpool of vice, all of these being acts for which a specific punishment has been decreed; in this sense, the prophets are completely free of all sin.
Another kind of sin might be called relative, for its commission does not entail any specific punishment Even this kind of sin is not to be expected from those true travellers on the path of God who are in direct communication with the source of all being and directly perceive all hidden truths. Given the vision with which they are endowed, it is not to be thought that they would be unaware of God for even an instant, for even such temporary inattention would diminish their closeness to God.
Considering the fact that these favored friends of God possess vast treasuries of faith and knowledge and have direct and precise awareness of reality, it will be considered a sin on their part if their orientation to God is interrupted for even a moment, even though such brief inattention would not occasion so much as a reproach in the case of lesser persons.
Something similar can be observed in the case of socially prominent people who carry certain titles and ranks; people have higher expectations of them than they do of others. Everyone is obliged to try to fulfil the expectations that others have of him, based on his rank and position ill society. Sobriety and dignity of speech are expected of a learned scholar, but not of an illiterate and unlearned man.
It is true that awareness of the undesirable consequences of sin does not in itself create immunity against sin and that its restraining influence is neither reliable nor constant. However, a knowledge that is deeply rooted and shows clearly all the grievous results of sin, a perception and an awareness that permits the reality of all things to be seen directly, in such a fashion that limitations of time and space are transcended, and a lively fear of severe punishment by God - all these taken together constitute a mechanism which makes the commission of a sin by a possessor of inerrancy impossible.
No intelligent pilot will consent to take off in a plane which he knows to be carrying a time bomb and is therefore destined to blow up in midair. It is not, however, that he has some immunity to this suicidal course of action built into him, involuntarily; he can freely decide whether to take off or not. The fact that he refrains from taking off is because he is fully aware of the disastrous consequences that would inevitably follow if he did; it is his intelligence and awareness that guide him and reduce to zero the possibility that he would do so.
This may serve as an illustration for the way in which profound and immediate knowledge of the fatal consequences of an act can provide immunity against committing that act, in the most powerful and practical way imaginable.
The leader of religion is not subject to compulsion or determination in his obeying divine command or adorning his soul with purity and virtue, nor does inerrancy negate his possession of free will and choice, in the sense of making it impossible for him to sin, without any involvement of his ability to decide.
It is rather that the Imams' constant orientation to the pure essence of God, their selfless struggles for His sake, their devotion, self-sacrifice, and exertions in seeking His satisfaction, powerfully insure these exalted personages against the commission of sin. Although- they retain the capacity for committing evil deeds, they never pollute themselves by committing them, and their minds never even incline in that direction.
Their comprehensive knowledge of the corruption caused by sin, joined to their thorough awareness of the sublimity of the divine essence, suffices fully to rein in any instinctual tendencies that might exist in their beings and to render them steadfast on the path of purity, piety, and virtue.
Quite apart from the Inerrant Imams, peace be upon them, who are of course situated at exalted levels of knowledge and insight, there are those who are not inerrant but are nonetheless sincere and ardent lovers of God who sacrifice their whole beings for His sake, and effectively acquire a degree of immunity from sin in their exertions to attain God's pleasure, so that the mere thought of disobeying divine command has no attraction for them.
It is of course possible that in their case the desired result is attained not by breadth of understanding or completeness of awareness, but by a strong sense of obedience to God, an innate purity of mind which quells any tendency to sin that may exist within them and leads them to a categorical rejection of evil.
The commission of a sin arises either from incomplete knowledge of the ugliness of the sin, unawareness of its evil consequences, deficiency of intelligence, or feebleness of the will when confronted with the onslaught of passionate desire. None of these factors can obtain in the case of one who possesses abundant spiritual knowledge, who perceives in detailed form all the corruption sin causes, and who has subordinated his ego to the demands of piety.
In addition, freedom from error and sin is ensured by the protection God extends for the sake of the correct conveyance of the message. In just the same way that God watches over the first receipt of revelation by the Prophet, peace and blessings be upon him and his family, in order to exclude all error, divinely guaranteed inerrancy is also called for at this stage in the process. For it is necessary that Cod's message and commands should be conveyed to mankind without the least error or mistake, whether intentional or accidental.
Thus the Qur'an says:
"Were it not for God's grace and mercy toward you, a group of God's enemies would have conspired to make you deviate from the right path. Thanks to God's kindness, it was only themselves that they caused to wander from the truth, and they are completely unable to harm you. God has bestowed on you this Book, wisdom and prophethood, and taught you what you knew not, for God's kindness to you is great and His favor unbounded." (4:111)
The propagation and implementation of God's revealed commands is similar, in that it is a prolongation of messengerhood and the leader and Imam to whom these tasks fall must like the Prophet be unassailably immune to error in his words, actions, and deeds. To commit any error in the exposition of God's commands would negate the whole purpose of the Imamate, in just the same way that corrupt and unworthy rulers are a threat to the authenticity of religion.
There can be absolutely no doubt that if the responsibility for preserving and implementing the laws of religion is not entrusted to a trustworthy and inerrant individual who heads the executive power and applies them faithfully and integrally, the aims and purposes of religion will suffer decay and distortion, for there is a possibility that an unreliable and errant individual who heads the executive power may implement the laws incorrectly or on the basis of incorrect knowledge, or deliberately distort in conformity with his personal desires and interests.
Furthermore, there are numerous verses of the Qur'an which call for elucidation and interpretation by the Imam; it is he who must supply the necessary clarifications.
One in whom all human perfections have been actualized is a complete human exemplar of the religion. He embodies the state that is the ultimate aim of man's evolution and is always situated on the straight path which leads in that direction. He is inherently bound to act in accordance with the shari'ah in every period of his life and is never polluted by sin or impurity at any point in his life. If even a brief portion of his life were to be spent in sin, resulting in a temporary deviation from the straight path, he could no longer be regarded as an exemplary individual, a perfect model of religion, and the divine aim of providing men with the means of ascent toward Him could not be realized.
It is impossible therefore to renounce the principle that the one who expounds and implements divine law must possess comprehensive inerrancy and freedom from sin, even before his actual assumption of the Imamate. Were it to be otherwise, society cold never submit to the guidance and instructions of the Imam with full confidence.
 al-Saduq, al-Amali, p. 376.