He who believes in and he who does not believe: the verb, though used with a preposition in the former and without it in the latter clause, can best be taken as having the same meaning in both, namely, “to give credence to,” or in this context, “to accept as true the witness of.” For a similar case of differentiation of form but identity of meaning, compare “believe in the name of” in 3.23 (where the Greek is without the preposition) and 5.13 (where it is with the preposition).
The interpretation given above of verse 10 is followed by several commentators and translators, but others suppose that the different constructions have different meanings. Those who see different meanings take verse 10a as referring to faith and trust in the power and nearness of the Son of God, and see in verse 10b a reference to not giving credence to God. In the opinion of the present authors, the parallelism existing between the positive clause in verse 10a and the negative one in verse 10b makes such differentiation less probable.
Has the testimony in himself, that is, accepts and keeps the testimony, pondering it, carrying it about, and holding fast to it. Testimony refers to the things God has declared to be true.
Has made him (that is, God) a liar, see comments on 1.10 and on “we lie” in 1.6. Here the verb is in the perfect tense, expressing that the act in the past affects the present. The perfect tense of the two following verbs has similar force.
He has not believed in the testimony …, or ‘he has not given credence to (or has not accepted as true) the testimony…’: This is yet another construction of the verb “to believe” in which the goal is an abstract noun, not a noun referring to a person as in verse 10b. Semantically speaking, however, believing in a God-given testimony (here) and believing God who gives a testimony (verse 10b) amount much to the same thing. Both must often be rendered in the same way.
The testimony that God has borne to his Son is in the Greek literally “the testimony God has testified about his Son.” In rendering such a combination of a verb with a related verbal noun, one must usually employ a more generic term, either for the verb (as does Revised Standard Version here, compare also, ‘the testimony that God has given’), or for the verbal noun; for example, ‘what God has attested (or said as witness),’ ‘the things God has declared to be true.’
Quoted with permission from Haas, C., de Jonge, M. and Swellengrebel, J.L. A Handbook on The First Letter of John. (UBS Handbook Series). New York: UBS, 1972. For this and other handbooks for translators see here .