In your law - Deuteronomy 17:6; Deuteronomy 19:15. Compare Matthew 18:16. This related to cases in which the life of an individual was involved. Jesus says that if, in such a case, the testimony of two men were sufficient to establish a fact, his own testimony and that of his Father ought to be esteemed ample evidence in the case of religious doctrine.
Two men - If two men could confirm a case, the evidence of Jesus and of God ought not to be deemed insufficient.
Is true - In Deuteronomy, “established.” This means the same thing. It is confirmed; is worthy of belief.