If anyone is willing to do a little summer reading, this is the most comprehensive study on prayer I have yet to come across.
I encourage anyone to put aside any doctrinal or Theological pre-conceptions and get fasten your seat-belt -- May The Holy Spirit bless you with wisdom and revelation in Jesus' Name.
Here is a sample:
1. FROM the previous part of the work we clearly see how completely destitute man is of all good, how devoid of every means of procuring his own salvation. Hence, if he would obtain succour (sweetness, relief, sucrose, sugar) in his necessity, he must go beyond himself, and procure it from some other quarter. It has farther been shown that the Lord kindly and spontaneously manifests himself in Christ, in whom he offers all happiness for our misery, all abundance for our want, opening up the treasures of heaven to us, so that we may turn with full faith to his beloved Son, depend upon him with full expectation, rest in him, and cleave to him with full hope. This, indeed, is that secret and hidden philosophy which cannot be learned by syllogisms: a philosophy thoroughly understood by those whose eyes God has so opened as to see light in his light (Ps. 36:9). But after we have learned by faith to know that whatever is necessary for us or defective in us is supplied in God and in our Lord Jesus Christ, in whom it hath pleased the Father that all fullness should dwell, that we may from thence draw, as from an inexhaustible fountain, it remains for us to seek and in prayer implore of him what we have learned to be in him. To know God as the sovereign disposer of all good, inviting us to present our requests, and yet not to approach or ask of him, were so far from availing us, that it were just as if one told of a treasure were to allow it to remain buried in the ground. Hence the Apostle, to show that a faith unaccompanied with prayer to God cannot be genuine, states this to be the order: As faith springs from the Gospel, so by faith our hearts are framed to call upon the name of God (Rom. 10:14). And this is the very thing which he had expressed some time before--viz. that the Spirit of adoption, which seals the testimony of the Gospel on our hearts, gives us courage to make our requests known unto God, calls forth groanings which cannot be uttered, and enables us to cry, Abba, Father (Rom. 8:26). This last point, as we have hitherto only touched upon it slightly in passing, must now be treated more fully.
2. To prayer, then, are we indebted for penetrating to those riches which are treasured up for us with our heavenly Father. For there is a kind of intercourse (exchange, conversation) between God and men, by which, having entered the upper sanctuary, they appear before Him and appeal to his promises, that when necessity requires, they may learn by experiences (answers) that what they believed merely on the authority of his word (at first), was not in vain. Accordingly, we see that nothing is set before us as an object of expectation from the Lord which we are not enjoined (encouraged, urged) to ask of Him in prayer, so true it is that prayer digs up those treasures which the Gospel of our Lord discovers to the eye of faith. The necessity and utility of this exercise of prayer no words can sufficiently express. Assuredly it is not without cause our heavenly Father declares that our only safety is in calling upon his name, since by it we invoke the presence of his providence to watch over our interests, of his power to sustain us when weak and almost fainting, of his goodness to receive us into favour, though miserably loaded with sin; in fine, call upon him to manifest himself to us in all his perfections. Hence, admirable peace and tranquillity are given to our consciences; for the straits (narrow channel of water difficult to navigate between dangerous shoals) by which we were pressed being laid before the Lord, we rest fully satisfied with the assurance that none of our evils are unknown to him, and that he is both able and willing to make the best provision for us.
3. But some one will say, Does he not know without a monitor both what our difficulties are, and what is meet for our interest, so that it seems in some measure superfluous (over-flow, unnecessary) to solicit him by our prayers, as if he were winking, or even sleeping, until aroused by the sound of our voice? Those who argue thus attend not to the end for which the Lord taught us to pray. It was not so much for his sake as for ours. He wills indeed, as is just, that due honour be paid him by acknowledging that all which men desire or feel to be useful, and pray to obtain, is derived from him. But even the benefit of the homage which we thus pay him redounds to ourselves. Hence the holy patriarchs, the more confidently they proclaimed the mercies of God to themselves and others felt the stronger incitement to prayer. It will be sufficient to refer to the example of Elijah, who being assured of the purpose of God had good ground for the promise of rain which he gives to Ahab, and yet prays anxiously upon his knees, and sends his servant seven times to inquire (1 Kings 18:42); not that he discredits the oracle, but because he knows it to be his duty to lay his desires before God, lest his faith should become drowsy or torpid (numb). Wherefore, although it is true that while we are listless or insensible to our wretchedness, he wakes and watches for us and sometimes even assists us unasked; it is very much for our interest to be constantly supplicating him; first, that our heart may always be inflamed with a serious and ardent (enflamed) desire of seeking, loving and serving him, while we accustom ourselves to have recourse to him as a sacred anchor in every necessity; secondly, that no desires, no longing whatever, of which we are ashamed to make him the witness, may enter our minds, while we learn to place all our wishes in his sight, and thus pour out our heart before him; and, lastly, that we may be prepared to receive all his benefits with true gratitude and thanksgiving, while our prayers remind us that they proceed from his hand. Moreover, having obtained what we asked, being persuaded that he has answered our prayers, we are led to long more earnestly for his favour, and at the same time have greater pleasure in welcoming the blessings which we perceive to have been obtained by our prayers. Lastly, use and experience confirm the thought of his providence in our minds in a manner adapted to our weakness, when we understand that he not only promises that he will never fail us, and spontaneously gives us access to approach him in every time of need, but has his hand always stretched out to assist his people, not amusing them with words, but proving himself to be a present aid. For these reasons, though our most merciful Father never slumbers nor sleeps, he very often seems to do so, that thus he may exercise us, when we might otherwise be listless and slothful, in asking, entreating, and earnestly beseeching him to our great good. It is very absurd, therefore, to dissuade men from prayer, by pretending that Divine Providence, which is always watching over the government of the universes is in vain importuned by our supplications, when, on the contrary, the Lord himself declares, that he is "nigh unto all that call upon him, to all that call upon him in truth" (Ps. 145:18). No better is the frivolous allegation of others, that it is superfluous to pray for things which the Lord is ready of his own accord to bestow; since it is his pleasure that those very things which flow from his spontaneous liberality should be acknowledged as conceded to our prayers. This is testified by that memorable sentence in the psalms to which many others corresponds: "The eyes of the Lord are upon the righteous, and his ears are open unto their cry," (Ps. 34:15). This passage, while extolling the care which Divine Providence spontaneously exercises over the safety of believers, omits not the exercise of faith by which the mind is aroused from sloth. The eyes of God are awake to assist the blind in their necessity, but he is likewise pleased to listen to our groans, that he may give us the better proof of his love. And thus both things are true, "He that keepeth Israel shall neither slumber nor sleep," (Ps. 121:4); and yet whenever he sees us dumb and torpid, he withdraws as if he had forgotten us.
4. Let the first rule of right prayer then be, to have our heart and mind framed as becomes those who are entering into converse with God. This we shall accomplish in regard to the mind, if, laying aside carnal thoughts and cares which might interfere with the direct and pure contemplation of God, it not only be wholly intent on prayer, but also, as far as possible, be borne and raised above itself. I do not here insist on a mind so disengaged as to feel none of the gnawings of anxiety; on the contrary, it is by much anxiety that the fervor of prayer is inflamed. Thus we see that the holy servants of God betray great anguish, not to say solicitude, when they cause the voice of complaint to ascend to the Lord from the deep abyss and the jaws of death. What I say is, that all foreign and extraneous cares must be dispelled by which the mind might be driven to and fro in vague suspense, be drawn down from heaven, and kept groveling on the earth. When I say it must be raised above itself, I mean that it must not bring into the presence of God any of those things which our blind and stupid reason is wont to devise, nor keep itself confined within the little measure of its own vanity, but rise to a purity worthy of God.
5. Both things are specially worthy of notice. First, let every one in professing to pray turn thither all his thoughts and feelings, and be not (as is usual) distracted by wandering thoughts; because nothing is more contrary to the reverence due to God than that levity which bespeaks a mind too much given to license and devoid of fear. In this matter we ought to labour the more earnestly the more difficult we experience it to be; for no man is so intent on prayer as not to feel many thoughts creeping in, and either breaking off the tenor of his prayer, or retarding it by some turning or digression. Here let us consider how unbecoming it is when God admits us to familiar intercourse to abuse his great condescension by mingling things sacred and profane, reverence for him not keeping our minds under restraint; but just as if in prayer we were conversing with one like ourselves forgetting him, and allowing our thoughts to run to and fro. Let us know, then, that none duly prepare themselves for prayer but those who are so impressed with the majesty of God that they engage in it free from all earthly cares and affections. The ceremony of lifting up our hands in prayer is designed to remind us that we are far removed from God, unless our thoughts rise upward: as it is said in the psalm, "Unto thee, O Lord, do I lift up my soul," (Psalm 25:1). And Scripture repeatedly uses the expression to raise our prayer, meaning that those who would be heard by God must not grovel in the mire. The sum is, that the more liberally God deals with us, condescendingly inviting us to disburden our cares into his bosom, the less excusable we are if this admirable and incomparable blessing does not in our estimation outweigh all other things, and win our affection, that prayer may seriously engage our every thought and feeling. This cannot be unless our mind, strenuously exerting itself against all impediments, rise upward.
This was a sampling... If you are pulled into reading further, the entirety of the Subject of Prayer, including holiness, righteousness by faith, perseverance & et cetera, can be found at the following link at Bible Study Tools...