St. John Climacus(+649 A.D.) on Prayer:
Prayer is by its very nature a dialogue and a union with God. Its effect is to hold the world together and to achieve a reconciliation with God. It is expiation of sin, a bridge over temptation, a barrier against affliction. It wipes out conflict, is the work of Angels and the nourishment of all bodiless beings. Prayer is the future gladness, an endless work, a wellspring of virtues, a source of grace, hidden progress, food for the soul, an illumination of the mind, an axe against despair, a proof of hope, sorrow done away with, the reduction of anger, the mirror of progress, a demonstration of success, evidence of one's condition, the future revealed, and a sign of glory. For him who truly prays, prayer is the court, the judgment hall and the tribunal of the Lord before the judgment to come.
Those of us about to stand before our King and God in order to speak with Him should not move into this without preparation, lest, seeing us from afar without weapons and clothing suitable for those who stand before the King, He should order his servants and slaves to bind us, to drive us out of His sight and to tear up our petitions and throw them in our face.
When you are going to stand before the Lord let the garment of your soul be woven throughout with the thread of wrongs suffered but forgotten. Otherwise, prayer will be of no benefit to you. Pray in all simplicity. For both the tax collector and the prodigal son were reconciled to God by a single phrase.
Before all else, let us list sincere thanksgiving first on the scroll of our prayer. On the second line, we should put confession and heartfelt contrition of soul. Then let us present our petition to the King of all. This is the best way of prayer, as it was shown to one of the monks by an angel of the Lord...
Do not be over-complicated in the words you use when praying, because the simple and unadorned lisping of the children has often won the heart of their Heavenly Father. Until we have acquired genuine prayer, we are like people teaching children to begin to walk.
After as long spell of prayer, do not say that nothing has been gained, for you have already achieved something. After all, what higher good is there than to cling to the Lord and to persevere in unceasing union with Him?... Prepare yourself for your set times of prayer by unceasing prayer in your soul, and you will soon make progress... Your prayer shows where you stand. Indeed, theologians say that prayer is one's mirror...
Hold on to the staff of prayer and you will not fall. And even a fall will not be fatal, since prayer is a devout coercion of God (c.f. Matt. 11:12)... 'I cried out with all my heart', says the Psalmist (Ps 118:145). He is referring to body, soul, and spirit; and where the last two are gathered, God is there in the midst of them (c.f. Matt. 18:20). We are not all the same, either in body or in soul. Some profit from singing the psalms quickly, others from doing so slowly... Always be brave, and God will teach you your prayer.
You cannot learn to see just because someone tell you to do so. You require your own natural power of sight. In the same way, you cannot discover from the teachings of others the beauty of prayer. Prayer has its own teacher in God, Who 'teaches us knowledge' (Ps 93:10) and grants prayer to those who pray and blesses the years of the just.