John 5:31

Ἐὰν εγὼ μαρτυρῶ … ἀληθής. Jesus anticipates the objection, that these great claims were made solely on His own authority [ἔγνω τοὺς Ἰουδαίους ἐνθυμουμένους ἀντιθεῖναι, Euthym.]. The Jewish law is given by Wetstein, “Testibus de se ipsis non credunt,” or “Homo non est fide dignus de se ipso,” and cf. Deuteronomy 19:15. The same law prevailed among the Greeks, μαρτυρεῖν γὰρ οἱ νόμοι οὐκ ἐῶσιν αὐτὸν ἑαυτῷ (Demosth., De Cor., 2), and among the Romans, “more majorum comparatum est, ut in minimis rebus homines amplissimi testimonium de sua re non dicerent” (Cicero, pro Roscio, 36, Wetstein). Grotius says: “Romani dicunt neminem idoneum testem esse in re sua”. But how can Jesus say that if His witness stands alone it is not true? Chrysostom says He speaks not absolutely but with reference to their suspicion [πρὸς τὴν ἐκείνων ὑπόνοιαν]. And on occasion He can maintain that His testimony of Himself is true, chap. John 8:13, where He says “Though I witness of myself my witness is true,” and demands that He be considered one of the two witnesses required. Here the point of view is different, and He means: Were I standing alone, unauthenticated by the Father, my claims would not be worthy of credit. But ἄλλος ἐστὶν ὁ μαρτυρῶν περὶ ἐμοῦ (on the definite predicate with indefinite subject vide Winer, p. 136). “It is another that beareth witness of me,” namely, the Father [σημαίνει τὸν ἐν τοῖς οὐρανοῖς ὄντα θεὸν καὶ Πατέρα, Cyril, Melanchthon, and the best modern interpreters, Holtzmann, Weiss, Westcott]. Grotius, following Chrysostom and Euthymius, says “facillimum est ut de Johanne sumamus, quia de eo sunt quae proxime sequuntur”. Against this is (1) the disclaimer of John's testimony, John 5:34; (2) and especially the accentuated opposition of ὑμεῖς, John 5:33, and ἐγώ, John 5:34. For other reasons, see Lücke. Of this witness Jesus says οἶδα ὅτι … ἐμοῦ. Why this addition? Is it an overflow of satisfaction in the unassailable position this testimony gives Him? Rather it is the offset to the supposition made in John 5:31, “my witness is not true”. [Cyril's interpretation is inexact, but suggestive: μονονουχὶ τοῦτο διδάσκων, ὅτι Θεὸς ὢν ἀληθινὸς, οἶδα, φησὶν, ἐμαυτὸν, κεχαρισμένον δὲ οὐδὲν ὁ Πατὴρ ἐρεῖ περὶ ἐμοῦ.]