Augustine of Hippo, on 1John 3:9

“Whosoever is born of God, committeth not sin: for his seed abideth in him, and he can not sin, because he is born of God.”

“In saying, "Whosoever is born of God sinneth not," it is probable he meant it of some particular sin: for else it will be contrary to that place: "If we say that we have no sin, we deceive ourselves, and the truth is not in us." In this way then the question may be solved. There is a certain sin, which he that is born of God cannot commit; a sin, which not being committed, other sins are loosed, and being committed, other sins are confirmed. What is this sin? To do contrary to the commandment of Christ, contrary to the New Testament. What is the new commandment? "A new commandment give I unto you, that ye love one another." Whoso doeth contrary to charity and contrary to brotherly love, let him not dare to glory and say that he is born of God: but whoso is in brotherly love, there are certain sins which he cannot commit, and this above all, that he should hate his brother. And how fares it with him concerning his other sins, of which it is said, "If we say that we have no sin, we deceive ourselves, and the truth is not in us?" Let him hear that which shall set his mind at rest from another place of Scripture; "Charity covereth a multitude of sins."”

Imported from an open dataset — not yet checked against the printed edition.