A cordial discipline of worship, especially the invoking worship, is "informing" [tafhim]. It is to take the heart, at the beginning, as a child not yet able to speak, and is wanted to be taught. So, each of the invocations, recitations, facts and secrets of worship is to be taught to the heart with strict accuracy and effort, and whatever the degree of perfection, one has to teach to the heart the facts which he has so far recognized. Even if one was unable to understand the meanings of the Qur'an and the invocations, and had no share of the secrets of worship, he, nevertheless, would have to teach his heart the very general meanings, such as telling it that the Qur'an is the words of Allah, that the invocations are remembrance of Allah, and that worship is obeying the Creator. He has to teach his heart such general information. Should he be of those who understand the apparent meanings of the Qur'an and the invocations, such as the promises, warnings, biddings and forbiddings, as well as the information about the Source [mabda'] and Resurrection [ma'ad], he must inform his heart of whatever has been understood from them by him. Should a fact of knowledge or a secret of worship be exposed to him, he is to inform it to his heart carefully and strictly. The result of such information is that after a period of perseverance the tongue of the heart will open to speaking and will become an invoker and a reminder. At the beginning the heart is a learner and the tongue a teacher. Whenever the tongue invokes, the heart also becomes an invoker, and so the heart is a follower of the tongue. But after that the heart's tongue learns to speak, the contrary happens: the heart becomes invoker and the tongue follows it in invocation and in movement. Rather, sometimes it happens that even when man is sleeping, his tongue starts invocating in pursuit of his heart's invocation, as the heart's invocation is not confined to the state of wakefulness, and when the heart remembers, the tongue, having become its follower, starts invocating after it, and it leaks out from the dominion of the heart: "Say: Every one acts according to his own manner ..." 
In short, at the beginning man must observe this discipline, that is, "informing", so that the tongue of the heart starts speaking, which is the real objective. The sign denoting that the heart's tongue has been released is that the tiredness and the hardship of the invocation are removed and replaced by animation and pleasure. It is like a baby which has not yet started talking, its tutor feels tired and bored before it speaks. No sooner the baby starts prattling than his tutor's fatigue goes away and the teacher follows up the child's utterances without tiredness or trouble. Similar is the heart. It is a mere infant at the start, knowing not how to speak. It is to be taught, and the invocations and the recitations are to be placed on its tongue. Then, as it begins talking, man begins to be its follower, and there will remain no pain of teaching nor any tiredness of invocating. This discipline is quite necessary for the beginners.
It must be noted that one of the secrets of repeating the invocations and benedictions and continuing the remembrance and worshipping is that the heart's tongue gets untied, and the heart becomes an invoking devotee. Without observing this discipline the tongue of the heart would remain tied up.
Some noble hadiths refer to this. The noble al-Kafi, quoting Imam as Sadiq (AS), who quoted Imam 'Ali (AS) who, referring to some disciplines of recitation, said: " ...But strike with it (the Qur'an) your hardened hearts, and do not be eager to get to the end of the surah. 
In another hadith in al-Kafi, Imam as Sadiq (AS) told Abu 'Usamah: "0 Abu 'Usamah, call your hearts [qulub] to remember Allah, and avoid what displeases Him." 
Even the most perfect godly men (AS) used to observe this discipline. A hadith relates that Imam as Sadiq (may Allah's peace be upon him) (once) was subject to a fit during the salat and fainted. When he came to his senses and he was asked about the reason, he said: "I kept repeating this ayah to my heart until I heard it from the one Who spoke it, and so, my body could not bear to see His power." 
Abu Dharr is quoted to have said that the Messenger of Allah (SA) was one night repeating this Qur'anic verse: "If You should torment them, then they are, indeed, Your servants, and if You should forgive them, then You are, indeed, the Mighty, the Wise." 
In short, the reality of invocation and remembrance is the invocation of the heart, without which the invocation of the tongue will be futile and worthless. This is referred to in a number of hadiths. The Messenger of Allah (SA) informed Abu Dharr: "Oh Abu Dharr, two rak'ats of salat in contemplation are better than spending the whole night with an inattentive (or forgetful) heart." 
The Messenger of Allah (SA) is also quoted to have said: "Allah, the Exalted, would not look at your faces, but at your hearts." 
In the hadiths concerning the presence of heart it is stated that, the more the presence of heart in the salat, the better it is accepted, and the more the negligence of the heart, the less it is acceptable. As long as the said discipline is not observed, no cordial invocation will happen, and the heart will not come out of its being inattentive and negligent.
It is narrated that Imam as Sadiq (A.S) said: "Make your heart a qiblah to your tongue and do not move it except by a sign from the heart."  But the heart would not become a qiblah, nor would the tongue and the other organs follow it unless the said discipline was observed. Should it happen without the observation of this discipline, it would be a rarity, and one must not take pride in it.
. Surah Isra': 84.
. Usulul Kafi, vol. 4, p. 418, Book on "The Merit of the Qur'an", ch. on "Reciting the Qur'an in a Sweet Voice", hadith 1.
. Al Kafi, (Raudah), Vol. 8, p. 167. Biharul Anwar, vol. 67 p. 59, Book on "Faith and Disbelief' ch. 44, hadith, 38.
. Al-Mahajjatul Bayda' vol. I. p. 352, Book on "The Secrets of the Salat", ch. on "The Merit of Submission and its Meaning".
. Surah al-Ma'idah: 118. Ruhul Ma'ani Tafsir al-Qur'an, by 'Allamah al-Alusi Vol. 7, p. 70, quoted from the Sunans of an-Nasai and al-Bayhaqi.
. Biharul Anwar, vol. 74, p. 82, Book of "Ar-Raudah" ch. on "The Prophet's Admonitions", hadith 2, quoted from Makarimul Akhlaq, p. 465.
. Ibid. And Biharul Anwar, vol. 67, p. 248, quoted from jami 'ul Akhbar, p. 117 (with a slight addition).
. Refer to footnote No.33.