1 John 5:9

If we receive the witness of men And it is notorious that we do so: comp. -if God so loved us" (1 John 4:11), and see on 2 John 1:10. The argument reads like an echo of that of Christ to the Pharisees, -In your law it is written that the witness of two menis true" (John 8:17); how much more therefore the witness of the Father and the Son? For -receive" in the sense of -accept as valid" comp. John 3:11; John 3:32-33.

for Or, because. Something is evidently to be understood; e.g. -I say, the witness of God, because…", or -I use this argument, because…".

this is the witness of God Better, as R.V., the witness of God is this: -this" is the predicate and refers to what follows (see on 1 John 1:5). His witness consists in His having borne witness about His Son.

which he hath testified According to the better reading and rendering, that He hath borne witness. -I appeal to the witness of God, because the witness of God is this, even the fact that He hath borne witness concerning His Son". The perfect tense indicates the permanence of the testimony. Comp. -He that hath seen hath borne witness" (John 19:35).