If one studies the literature of Islam carefully, one will immediately encounter a vast and varied field of material.
First there is the network of laws and regulations which makes up Islamic jurisprudence (fiqh) and which takes into consideration and regulates man's every individual and social "movement and rest", activity and situation, at every moment of time, in every place and under all conditions, as well as every particular and general occurrence related to human life.
Second there is a vast range of moral and ethical expositions which weighs every sort of moral activity, whether praiseworthy or blamable, and presents as a model for human society that which befits the perfection of man.
Finally on the level of Islam's overall view of Reality there is the general "philosophy" of Islam, that is, its sciences relating to cosmology, spiritual anthropology and finally the knowledge of God, presented in the clearest possible expression and most direct manner.
On a more profound level of study and penetration it will become obvious that the various elements of this tradition, with all their astonishing complexity and variety, are governed by a particular kind of interrelationship; that all of these elements are reducible in the final analysis to one truth, the "Profession of God's Unity" (tawhid), which is the ultimate principle of all the Islamic sciences.
"A good word is as a good tree—its roots are in heaven, it gives its produce every season by the leave of its Lord" (Quran 14 : 24).
The noble sayings and writings presented in the present work were selected and translated from the traditions left by the foremost exponents of Islam. They include expositions elucidating the principle of tawhid and making clear the fundamental basis of all Islamic sciences and pursuits.
At the same time they contain excellent and subtle allusions to the manner in which the important remaining sciences are ordered and organized around tawhid, how the moral virtues are based upon it, and how finally the practical aspects of Islam are founded upon and derived from these virtues. Finally, 'Ali's "Instructions to Malik al-Ashtar" clarify the general situation of Islamic society in relation to the practical application of Islamic government.
All the traditions translated in the present work are summarized in the following two sentences: "Islam is the religion of seeing things as they are" and "Islam means to submit to the Truth (al-haqq) and to follow It in one's beliefs and actions."
Allamah Sayyid Muhammad Husayn Tabataba'i