Andreas of Caesarea : After giving us one testimony about his Son, God gave us another, which is eternal life. — CATENA Bede : He who believes in the Son of God has the testimony of God in himself. He who thus believes in the Son of God, so as to practice in work what he believes, has the testimony of God in himself. Surely this is because he also may rightly be counted among the number of the sons of God, as the only Son of God promises to his faithful: "If anyone serves me, the Father will honor him" (John 12). If you have deserved to have the testimony of God, if you possess God as a witness of your unblemished faith, what does the infamy of men, what does even persecution harm you? For if God is for us, who can be against us? — Commentary on the Catholic Epistles Bede : Whoever does not believe in the Son makes him a liar, etc. In vain the Jews and heretics think they believe in and venerate the Father, as long as they despise Christ and refuse to believe in him. For he who does not honor the Son does not honor the Father who sent him. Those who do not believe in the Son, who says "I and the Father are one" (John 10), and when Caiaphas asked, "Are you the Christ, the Son of the Blessed?" (Mark 14), he replied: "I am" (ibid.); but they argue that he is either not the Christ, or not the Son of God, or not similar to the Father, they certainly make the Father a liar, because they do not believe the testimony he has testified about his Son: namely, in what I mentioned before: "You are my beloved Son, in you I am well pleased" (Luke 3); and even in what he testified when the hour of passion was imminent, while he was praying and saying: "Father, save me from this hour, but for this cause I came to this hour. Father, glorify your name" (John 12), he responded, even the crowd hearing from heaven, "I have both glorified it and will glorify it again" (ibid.), truly signifying himself as God the Father in the heavens of him who, as a true man, was about to suffer death on earth. — Commentary on the Catholic Epistles Hilary of Arles : God can never turn himself into a liar, because he is the essence of truth. But an unbelieving man is a liar, because he does not believe in the truth of God. — INTRODUCTORY COMMENTARY ON 1 JOHN Oecumenius : He who believes in the Son of God has the testimony in himself. He who does not believe God has made him a liar, because he does not believe the testimony that God has given of his Son. And this is the testimony, that God has given us eternal life: and this life is in his Son. Therefore, whoever believes in the Son of God, that He is God as the Son of God, has testimony in himself, that is, in himself, believing that he too has been adopted by God through Jesus, the adopted one. Whoever does not believe the truth is subject to two evils, namely disbelief, making God a liar: and furthermore depriving himself of adoption, and thus also of eternal life, which Christ has promised to those who would be adopted by Him: which he also has in himself as it is written in the Gospel: "In Him was life." (Jn. 1:4) — Commentary on 1 John