Judaism teaches that at the core of each prayer is a heart in emotional exchange with the Creator. Over time, three general forms of prayer developed. Each form is an expression of a different aspect of the heart. The three forms are: recitals of Psalms, liturgical prayers and informal conversations with the Creator. The recitals of Psalms seem to be an expression of mind resonating within the heart. Liturgical prayers seem to be an exposure of the inner heart within the heart - a purified core of heart. And informal conversations seem to be expressions largely projecting from the heart’s outer surface - the body of the heart.
The heart, as a whole, is lodged between the mind and body. In psychological terms, the emotional self occupies the space between the intellectual and kinesthetic selves. Therefore, on one of her sides, the heart tends towards the intellectual side of the border. While on her other side, she tends towards the kinesthetic side of the border. At each side, what’s just over the border can already be felt.
The key for understanding which form of prayer matches with which aspect of the heart is the potency of Torah found in the prayer. Torah study is intellectual devotion. So the more potent the prayer’s Torah content, the closer the prayer is to the heart’s intellectual pole. On the other hand, the less potent the Torah content, the closer the prayer is to the heart’s bodily pole. Naturally, what’s purely heart occupies the center of this spectrum.
The Psalms are the expression of the heart’s intellectual side; as the Psalms were composed with Biblical prophecy and therefore, are part of the scripture itself. They are intended not only for prayer, but, also for devotional study. In Psalms, the heart is carried by the absolute truths of Scripture, even while caught in the stormy waves of emotional reverie.
The liturgy is an expression of the heart’s pure emotional side, as it written as prayers for the masses. It is designed for everyone to emotionally connect to each other as a community and pour out a collective heart in prayer. The Torah content in the liturgy is a step removed from the Bible. All the words are either Biblical excerpts or paraphrases. Mostly, the person in prayer is not reading the Scripture directly, but, largely an echo of Scripture. Unlike Scripture, the central prayer, the Amidah, was not prophetically composed. Rather, it was composed via the holy spirit - a lower level of divine communion than prophecy.
This is not surprising since “spirit” is the aspect of the soul which operates through the heart. It’s the soul’s emotional level. So holy spirit is the human spirit emoting in a highly elevated state of holiness. This state would be ideal for composing a prayer designed to express the best of the human heart.
Informal conversations seem to express the body within the heart. These free flowing conversational prayers seem to mainly flow from divine guidance. Divine guidance is a lesser level than attaining a state of holy spirit. It simply means that whether or not the person is aware of it, his/her thoughts, speech and actions are being divinely guided.
It makes sense that free flowing conversational prayer would be more directly associated with the body within the heart than the other two kinds of prayer because (a) these conversations tend to come from the a more surface level of heart, i.e. the body of the heart and (b) they tend to very often revolve around the practicalities of the life situation on the ground. These features end up making this form of prayer the most user friendly of all the three forms to practice, as the subject matter tends to be about what the person in prayer relates to best.
Obviously, what’s described here is a relative scale. What for our level seems to be considered “prophetically driven” for the Psalmist’s own level might have been merely coming from his heart’s surface level. Indeed, Rebbe Nachman of Breslov relates that the Psalms of King David were culled from his free flowing conversational prayers. Similarly, for the group of ancient Rabbis who composed the centerpiece of Jewish liturgy, the Amidah. Such prayers might have been regarded by them as mere conversational prayers, though to our own level the Amidah appears as a fruit ripened on the tree of their holy spirit - much beyond anything the surface of our hearts can attain to.