3 “Jesus, therefore,” as the evangelist proceeds to say, “knowing all things that should come upon Him, went forth and says unto them, Whom do you seek? They answered Him, Jesus of Nazareth. Jesus says unto them, I am [He]. And Judas also, who betrayed Him, stood with them. As soon then as He had said unto them, I am He, they went backward, and fell to the ground.” Where now were the military cohort, and the servants of the chief men and the Pharisees? Where the terror and protection of weapons?
His own single voice uttering the words, “I am [He],” without any weapon, smote, repelled, prostrated that great crowd, with all the ferocity of their hatred and terror of their arms. For God lay hid in that human flesh; and eternal day was so obscured in those human limbs, that with lanterns and torches He was sought for to be slain by the darkness. “I am [He],” He says; and He casts the wicked to the ground. What will He do when He comes as judge, who did this when giving Himself up to be judged?
What will be His power when He comes to reign, who had this power when He came to die? And now everywhere through the gospel Christ is still saying, “I am [He];” and the Jews are looking for antichrist, that they may go backward and fall to the ground, as those who have abandoned what is heavenly, and are hankering after the earthly. It was for the very purpose of apprehending Jesus that His persecutors accompanied the traitor: they found the One they were seeking, for they heard, “I am [He].”
Why, then, did they not seize Him, but went backward and fell, but just because so He pleased, who could do whatever He pleased? But had He never permitted them to apprehend Him, they would certainly not have done what they came to do, but no more would He be doing what He came to do. They, verily, in their mad rage, sought for Him to put Him to death; but He, too, in giving Himself to death, was seeking for us. Accordingly, having thus shown His power to those who had the will, but not the power, to hold Him; let them now hold Him that He may work His own will with those who know it not.
Source: Tractates on the Gospel of John (New Advent)