18 To neglect these things any further, and to persevere in the former error, what is it else than to fall under the Lord's rebuke, who in the l psalm reproves, and says, “What have you to do to declare my statutes, or that you should take my covenant into your mouth, seeing you hate instruction and castest my words behind you? When you saw a thief, you consented with him, and hast been partaker with adulterers.” For to declare the righteousness and the covenant of the Lord, and not to do the same that the Lord did, what else is it than to cast away His words and to despise the Lord's instruction, to commit not earthly, but spiritual thefts and adulteries?
While any one is stealing from evangelical truth the words and doings of our Lord, he is corrupting and adulterating the divine precepts, as it is written in Jeremiah. He says, “What is the chaff to the wheat? Therefore, behold, I am against the prophets, says the Lord, who steal my words every one from his neighbour, and cause my people to err by their lies and by their lightness.” Also in the same prophet, in another place, He says, “She committed adultery with stocks and stones, and yet for all this she turned not unto me.” That this theft and adultery may not fall unto us also, we ought to be anxiously careful, and fearfully and religiously to watch.
For if we are priests of God and of Christ, I do not know any one whom we ought rather to follow than God and Christ, since He Himself emphatically says in the Gospel, “I am the light of the world; he that follows me shall not walk in darkness, but shall have the light of life.” Lest therefore we should walk in darkness, we ought to follow Christ, and to observe his precepts, because He Himself told His apostles in another place, as He sent them forth, “All power is given unto me in heaven and earth.
Go, therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: teaching them to observe all things whatsoever I have commanded you.” Wherefore, if we wish to walk in the light of Christ, let us not depart from His precepts and monitions, giving thanks that, while He instructs for the future what we ought to do, He pardons for the past wherein we in our simplicity have erred. And because already His second coming draws near to us, His benign and liberal condescension is more and more illuminating our hearts with the light of truth.
Source: The Epistles of Cyprian (New Advent)