Albert Barnes Commentary John 18:31

"Pilate therefore said unto them, Take him yourselves, and judge him according to your law. The Jews said unto him, It is not lawful for us to put any man to death:" — John 18:31 (ASV)

Judge him. The Jews had not directly informed him that they had judged him and pronounced him worthy of death. Pilate therefore told them to investigate the case: to ascertain the proof of his guilt, and to decide according to what the law of Moses prescribed.

It has been questioned whether this granted them the authority to execute him, or if it was merely an instruction to investigate the case and, if they found him guilty, to impose the lesser punishment they were still permitted to inflict on criminals. Probably the former was intended.

Since they had already determined that, in their view, this case demanded the death penalty, in their answer to Pilate they implied that they had pronounced on it, and that he ought to die. They still, therefore, pressed the matter on his attention and refused to obey his command to judge him.

It is not lawful for us to put anyone to death. The Jews were accustomed to putting people to death by mob action (Acts 7:59–60), but they did not have the authority to do so in any case through a regular judicial process. When they first made the plan to arrest the Savior, they did it to kill him (Matthew 26:4); but whether they intended to do this secretly, by mob action, or with the approval of the Roman governor, is uncertain.

The Jews themselves state that the authority to inflict capital punishment was taken away about forty years before the destruction of the temple. Nevertheless, it is probable that in the time of Christ, they had the authority to decide capital cases in matters related to religion (Josephus, Antiquities, book 14, chapter 10, section 2; compare to Jewish Wars, book 6, chapter 2, section 4).

In this instance, however, it is assumed that their sentence was to be confirmed by the Roman governor. But it is universally admitted that they did not have this authority in cases of sedition, riots, or treason against the Roman government. If they possessed this authority in cases of blasphemy and irreligion, they did not dare to exercise it here, because they feared a riot among the people (Matthew 26:5); therefore, they sought to involve Pilate's authority.

To achieve this, they endeavored to make it appear that it was a case of sedition and treason, and one that therefore demanded the intervention of the Roman governor. For this reason, it was on this charge that they arraigned him (Luke 23:2). In this way, a riot could be avoided, and they expected the odium of putting him to death would fall not on themselves, but on Pilate.