1. RABASH, Article No. 37 (1985), "Who Testifies to a Person?"
A prayer is called “a deficiency,” and he wants his deficiency to be filled. And yet, no deficiency is sensed in a person’s mouth; rather, all of man’s sensations are sensed in the heart. This is why if a person doesn’t feel a lack in his heart, what he utters in his mouth does not count at all, so we could say that he truly needs what he is asking for with his mouth. This is so because the filling he is asking for should enter a place of deficiency, which is the heart. This is why our sages said that a prayer should be from the bottom of the heart, meaning that the whole heart will sense the lack for which he is asking.
2. RABASH, Article No. 600, “From the Depth I Called You, Lord – 1”
it is written, “From the depth I called You, Lord,” meaning “I called You from the depth of trouble.” Hence, a person should think before the prayer how big is the lack in him, so the Creator will help him on a big deficiency.
It follows that one should pay attention in order to feel one’s lack. This is called “a prayer from the bottom of the heart” from the perspective of the receiver. However, there is also the matter of minding the Giver. That is, one should have great faith that the Creator will help him.
3. RABASH, Article No. 10 (1986), "Concerning Prayer"
The corporeal nature that we were given is such that through it we learn spiritual matters. Therefore, before one knows that he cannot obtain the vessels of bestowal by himself, he does not ask the Creator to give them to him. It follows that he does not have a real desire for the Creator to answer his prayer.
For this reason, one must work to obtain the vessels of bestowal by himself, and after all the work that he has put into it without obtaining it begins the real prayer from the bottom of the heart. At that time he can receive help from above, as our sages said, “He who comes to purify is aided.”
4. Baal HaSulam, Shamati, Article No. 5, "Lishma Is an Awakening from Above, and Why Do We Need an Awakening from Below?"
The prayer must be a complete prayer, from the bottom of the heart. This means that one knows one hundred percent that there is no one in the world who can help him but the Creator Himself.
Yet, how does one know this, that no one will help him but the Creator Himself? One can acquire that awareness precisely if he has exerted all the powers at his disposal and it did not help him. Thus, one must do every possible thing in the world to attain “for the sake of the Creator.” Then one can pray from the bottom of the heart, and then the Creator hears his prayer.
5. RABASH, Article No. 11 (1986), "A Real Prayer Is over a Real Deficiency"
There are two conditions for praying from the bottom of the heart: 1) His work must be against nature. That is, he wants to do everything only to bestow, and wants to exit self-love. At that time it can be said that he has a lack. 2) He begins to exit self-love by himself and exerts in it, but cannot move an inch from his state. At that time he becomes needy of the Creator’s help and his prayer is real
6. RABASH, Article No. 9 (1990), “What Is, ‘A Ladder Is Set on the Earth, and Its Top Reaches Heaven’, in the Work?”
The question is, Why does a person sometimes want to cancel the will to receive for himself? That is, many times he sees that when he asks the Creator to give him vessels of bestowal, the whole body resists, and his prayer is only lip-service, meaning only empty words. Yet, he sees that there are times when he can pray wholeheartedly. The answer is that this is already the answer to the prayer, meaning that the Creator gave him the strength to pray for this with all his heart. Therefore, a person must be hopeful that the Creator will bring him closer.
7. Maimonides, Mishneh Torah
How is there intention? One should clear his heart from all the thoughts and see himself as though he is standing before the Shechina [Divinity]. Therefore, one should settle oneself a little prior to the prayer, to aim his heart, and then pray. The first Hassidim [adherents of the Hassidut movement] would spend one hour prior to the prayer, one hour after the prayer, and extend the prayer by one hour.
8. Baal HaSulam, Shamati, Article No. 209, "Three Conditions in Prayer"
Prayer means “lost in the heart.” The more one is lost, so is the measure of his prayer. Clearly, one who lacks luxuries is not like one who has been sentenced to death, and only the execution is missing, and he is already tied with iron chains, and he is standing and pleading for his life. He will certainly not rest or sleep or be distracted for even a moment from praying for his life.
9. RABASH, Article No. 25 (1987), "What Is Heaviness of the Head in the Work?"
The primary goal should be to be rewarded with Dvekut [adhesion] with the Creator. Since the reason objects to this, he must go against reason, and this is very hard work.
Since he is asking the Creator to give him something to which all of his organs object, it follows that each and every prayer he makes to the Creator has its special work. This is why a prayer is called “work in the heart”.
10. RABASH, Article No. 10 (1986), "Concerning Prayer"
Our sages said, “‘And you shall work’ is prayer, the work in the heart.” By this we will understand why they refer to prayer as “work in the heart.” It is because one must work a lot on himself to cancel self-love and assume the work of obtaining vessels of bestowal. It follows that on the desire to have vessels of bestowal he must work with himself to want to pray, to be given the force of bestowal.