The text in the Epistle evidently points to that in the Gospel. The question is whether it outruns the Gospel in explicitness, as St Thomas argues, or keeps close within the textual lines of the former writing. The Vulgate, which St Thomas follows, differs from the Greek text in three particulars. (a) For the true God, the Greek is simply ton alêthinon him who is true. (6) For and be, the Greek is kai esmen, and we are. (c) For in his true Son, the Greek is en tô alêthinô, en tô huiô autou, in him who is true, in his Son. The literal rendering of the Greek, et sumus in vero, infilio ejus, would easily slip into the present Vulgate, et sumus in vero, filio ejus. Critically, the Greek is the true reading. It means, 'and we are united with Him who is true, by being united with His Son,' or, 'through His Son.' But in the next clause, Hic est verus Deus, what is the antecedent of the pronoun this? The Fathers, in controversy with the Arians, refer the pronoun to His Son Jesus Christ. Others take the clause for a summing of and repetition of what has been said, much in the manner of St John. They refer the pronoun houtos therefore to ton alêthinon and tô alêthinô, him who is true. They point to the next clause, Keep yourselves from idols, and will have it that St John is not occupied here with the divinity of the Son, but with the divinity of the one true God in contradiction with idols, by worshipping which the whole world then lay in the power of the evil one. A Catholic's faith in the divinity of his Lord is not all staked on one pronoun. He can afford to be just, or even generous, to an Arian.
Of God and His Creatures: 4.8