Andreas of Caesarea : Even at the end of his letter, John never stops insisting on the need for right doctrine. We have been given understanding to the extent that we have known the Son of God, who really has come into the world. This is what it means to say that "we have the mind of Christ." The person who has this mind and understanding knows what is really true and is united with him because he shares the same mind. — CATENA Augustine of Hippo : When ye read, "That we may be in His true Son Jesus Christ," think of the "true Son" of God. But this Son ye in no wise think to be the true Son of God, if ye deny Him to be begotten of the substance of the Father. For was He already Son of Man and by gift of God became Son of God, begotten indeed of God, but by grace, not by nature? Or, though not Son of Man, yet was He some sort of creature which, by God's changing it, was converted into Son of God? If you mean nothing of this sort, then was He either begotten of nothing, or of some substance. But thou hast relieved us from all fear of having to suppose that you affirm the Son of God to be of nothing, for thou hast declared that this is not your meaning. Therefore, He is of some substance. If not of the substance of the Father, then of what? Tell me. But ye cannot find any other. Consequently, the Father and the Son are of one and the same substance. This is the Homousion. — Ten Homilies on 1 John 10 Augustine of Hippo : In the Scriptures both you and We read, "That we may be in His true Son Jesus Christ; He is the true God and Eternal Life." Let both parties yield to such weighty evidence. Tell us then, whether this "true Son" of God, discriminated as He is by the property of this name from those who are sons by grace, be of no substance or of some substance. Thou sayest, "I do not say that He is of no substance, lest I should say that He is of nothing." He is therefore of some substance: I ask, of what? If not of the substance of the Father, seek another. If thou findest not another, as indeed thou canst find none at all, then acknowledge it to be the Father's, and confess the Son Homousios, "of one substance with the Father." — Ten Homilies on 1 John 10 Augustine of Hippo : Flesh is begotten of flesh, the Son of flesh is begotten of the substance of the flesh. Set aside corruption, reject from the eye of the mind all carnal passions, and behold "the invisible things of God understood by the means of the things that are made." Believe that the Creator who hath given flesh power to beget flesh, who hath given parents power of the substance of the flesh to generate "true sons" of flesh, much more had power to beget a "true Son" of His own substance, and to have one substance with the true Son, the spiritual incorruption remaining and carnal corruption being altogether alien therefrom. — Ten Homilies on 1 John 10 Augustine of Hippo : If He is begotten, He is Son: if He is Son, He is the "true Son," because Only-Begotten. For we also are called sons: He Son by nature, we sons by grace. To say that because He is begotten, He is of another nature, is to deny that He is the "true Son." Now we have the Scripture: "That we may be in His true Son Jesus Christ; He is the true God and Eternal Life." Why "true God"? because "true Son" of God. For if He has given to animals this property, that what they beget shall be none other than what they themselves are: man begets man, dog begets dog, and should God not beget God? If then He is of the same substance, why callest thou Him less? — Ten Homilies on 1 John 10 Augustine of Hippo : Is it because when a human father begets a son, though human beget human, yet greater begets less? If so, then let us wait for Christ to grow as human beings grow whom human beings beget! But if Christ, ever since He was begotten (and this was not in time but from eternity), is what He is, and yet is less than the Father, at that rate the human condition is the better of the two: for a human being at any rate can grow, and has the property of sooner or later attaining to the age, to the strength of the father; but He never: then how is He a "true Son"? — Ten Homilies on 1 John 10 Augustine of Hippo : And if the Son be not of the same substance as the Father, then is He a made substance: if a made substance, then not "all things were made by Him:" but, "all things were made by Him;" therefore, He is of one and the same substance with the Father. And therefore, not only God, but True (or, Very) God. Which the same John doth most openly affirm in his epistle: "We know that the Son of God is come; and hath given us an understanding that we may learn to know the True God, and may be in His true Son Jesus Christ. This is the True God and Eternal Life." — Ten Homilies on 1 John 10 Augustine of Hippo : Hence also by consequence we understand, that what the apostle Paul saith, "Who only hath immortality," he saith not merely of the Father, but of the One and Only God, which the Trinity itself is. For neither is the "Eternal Life" itself mortal in respect of any mutability: and consequently, since the Son of God "is Eternal Life," He also is to be understood together with the Father, where it is said, "Who only hath immortality." — Ten Homilies on 1 John 10 Bede : And we know that the Son of God has come, etc. For what could be clearer than these words? What could be sweeter? What could be said more strongly against all heresies? Christ is the true Son of God. The Father of Christ Jesus our Lord is the true God. The eternal Son of God came temporally into the world, who was in the world, and through whom the world was made. Nor did He come for any other reason than for our salvation, that is, to give us the understanding to know the true God. For no one could come to life without divine knowledge, no one could know God except by His teaching: as He Himself says: And no one knows the Son except the Father, nor does anyone know the Father except the Son, and whom the Son wills to reveal Him (Luke X). It is implied: both the Father and the Son. For the Son reveals both, who, appearing visibly in the flesh, has deigned to now reveal the secrets of divinity through His Gospel. — Commentary on the Catholic Epistles Bede : This is the true God, and eternal life. He had said that the Son is the true God, and repeatedly affirms that this one is the true God. He says that this one is eternal life. Not in the way eternal life is promised to us, which takes us from time and places us so that we never cease living well; but the Son is life, always remaining without the beginning of time, always remaining without end. — Commentary on the Catholic Epistles Clement of Alexandria ((as quoted by Cassiodorus)) : "And the Son of God has come and given us understanding," which comes to us, that is, by faith, and is also called the Holy Spirit. — From the Latin Translation of Cassiodorus Didymus the Blind : The understanding which God gave, by which it is known that the true Son of God is coming, is the same as the mind of Christ. — COMMENTARY ON 1 JOHN Oecumenius : And we know that the Son of God has come and has given us an understanding, that we may know Him who is true; and we are in Him who is true, in His Son Jesus Christ. This is the true God and eternal life. But since, John says, the Son of God has come and has given us an understanding by which we may know the true God through internal understanding, and be in His true Son Jesus Christ: we have come to know through this glory that He is the true God and eternal life, and by knowing we are safe from the onslaught of evil and its offenses. "This is the true God." This, also, serves as a demonstrative article. Here, the article indicates relationship. — Commentary on 1 John