The law they mean, is the law for putting false prophets to death, Deuteronomy 18:20. By the Son of God here, they mean the eternal Son of God, in all things equal with his Father; otherwise it was a term applicable to themselves, whom God calls his son, his firstborn, &c. Now for any in this sense to arrogate to himself this title who indeed was not so, was blasphemy, and that in the highest degree, and brought him under the notion of a false prophet of the deepest dye: but this was injuriously applied to Christ, who thought it no robbery to be equal with the Father, and who was so declared by God himself at his baptism and transfiguration; and who had made his Divine power appear by such works as no mere man ever did.
Related Commentaries of John 19:7
John 19:7
7 The Jews answered him, We have a law, and by our law he ought to die, because he made himself the Son of God.