Luke 22:51

‘But Jesus answered and said, “Allow them to go thus far.” And he touched his ear, and healed him.'

But Jesus stepped in on the side of the law and commanded that there be no interference with His arrest. It was after all something that they had a right to do if only they had gone about it in the correct manner. This far they must be allowed to go. And He reached out and touched the man's ear, which was probably hanging there limply, possibly on a sliver of flesh. The result was complete healing. This would ease the situation as the sight of a wounded and bleeding man must probably have caused the Roman chiliarch to take more widespread action if he had seen it when he came up. It would have made the situation appear more immediately serious.