Charles Ellicott Commentary John 19:7

"The Jews answered him, We have a law, and by that law he ought to die, because he made himself the Son of God." — John 19:7 (ASV)

We have a law, and by our law he ought to die.—The better reading is ... and by the law He ought to die. . They feel the bitter sarcasm of Pilate’s taunt, and appeal to their own law, which, in accordance with the general Roman policy, was in force in all questions which did not directly affect the Government. They change the accusation then from one of treason against Caesar (John 19:12), of which Pilate claimed to be judge, to one of blasphemy against God, of which they only could be judges; and assert that Jesus is by that law guilty of a capital offence, for which He ought to die. (Compare to Matthew 26:63-66 and Luke 22:70).