Benjamin Morgan Palmer, the pastor of First Presbyterian Church in New Orleans from 1856-1902, wrote a beautiful volume on the theology of prayer, as viewed in the religion of nature and under the covenant of grace. You can find it for free here. To whet your appetite, here is a snippet:
In the last analysis, then, what is prayer but the language of creaturely dependence upon that God from whom being itself is derived? ... This consciousness of dependence finds its only full expression in prayer; we lean upon God, and are at rest. It may pour itself forth with a pathos that stirs the heart of sympathy, or despair may muffle 'the groanings which cannot be uttered'; in either case the intelligent recognition of creature-helplessness leaning upon divine power is the kneeling posture of the soul in prayer. It is the thirst of ignorance drinking deep draughts from the overflowing fulness of divine wisdom. It is the exhaustion of weakness drawing nerve into a broken will from the resources of infinite strength. This is prayer: when, sinking through the earthly crust, the creature seeks repose in God; when from the eternal fountain he derives the help and solace which the creature always needs, and which the Creator alone can supply. (15-17)
It gets even better. So spend some time this weekend reading this book - you will be thankful you did.