Virtues are formed by prayer. Prayer preserves temperance, suppresses anger, restrains pride and envy, draws down upon the Holy Spirit into the soul and raises man to heaven.

[Mar Ephraim the Syrian, Moore, Orthodox Prayer]

Prayer is by nature a dialogue between man and God. It unites the soul with its Creator and reconciles the two. Its effect is to hold the world together.

[John of the Ladder, Ladder of Divine Ascent]

We must also know, beloved brethren, that every secret converse, every good care of the intellect directed toward God and every meditation upon spiritual things is delimited by prayer, is called by the name of prayer, and under its name is comprehended; whether you speak of various readings, or the cries of a mouth glorifying God, or sorrowing reflection on the Lord, or making bows with the body, or psalmody in verses, or all other things from which the teaching of genuine prayer comes. From genuine prayer, the love of God is born, for love comes of prayer.

[Mar Isaac the Syrian, Homily 63, Ascetical Homilies]