2 He, among the rest of His salutary admonitions and divine precepts wherewith He counsels His people for their salvation, Himself also gave a form of praying— Himself advised and instructed us what we should pray for. He who made us to live, taught us also to pray, with that same benignity, to wit, wherewith He has condescended to give and confer all things else; in order that while we speak to the Father in that prayer and supplication which the Son has taught us, we may be the more easily heard.
Already He had foretold that the hour was coming “when the true worshippers should worship the Father in spirit and in truth;” and He thus fulfilled what He before promised, so that we who by His sanctification have received the Spirit and truth, may also by His teaching worship truly and spiritually. For what can be a more spiritual prayer than that which was given to us by Christ, by whom also the Holy Spirit was given to us? What praying to the Father can be more truthful than that which was delivered to us by the Son who is the Truth, out of His own mouth? So that to pray otherwise than He taught is not ignorance alone, but also sin; since He Himself has established, and said, “You reject the commandments of God, that you may keep your own traditions.”
Source: The Treatises of Cyprian (New Advent)