28 What wonder is it, beloved brethren, if such is the prayer which God taught, seeing that He condensed in His teaching all our prayer in one saving sentence? This had already been before foretold by Isaiah the prophet, when, being filled with the Holy Spirit, he spoke of the majesty and loving-kindness of God, “consummating and shortening His word,” He says, “in righteousness, because a shortened word will the Lord make in the whole earth.” For when the Word of God, our Lord Jesus Christ, came unto all, and gathering alike the learned and unlearned, published to every sex and every age the precepts of salvation He made a large compendium of His precepts, that the memory of the scholars might not be burdened in the celestial learning, but might quickly learn what was necessary to a simple faith.
Thus, when He taught what is life eternal, He embraced the sacrament of life in a large and divine brevity, saying, “And this is life eternal, that they might know You, the only and true God, and Jesus Christ, whom You have sent.” Also, when He would gather from the law and the prophets the first and greatest commandments, He said, “Hear, O Israel; the Lord your God is one God: and you shall love the Lord your God with all your heart, and with all your mind, and with all your strength. This is the first commandment. And the second is like it, You shall love your neighbour as yourself.” “On these two commandments hang all the law and the prophets.” And again: “Whatsoever good things you would have men do to you, do even so to them. For this is the law and the prophets.”
Source: The Treatises of Cyprian (New Advent)