2 With these preliminary remarks, I think that we shall not have to labor much for the meaning in this chapter; for that is often betokened in the head which was to be in the body. “After these things,” says he, “Jesus walked in Galilee: for He would not walk in Judea, because the Jews sought to kill Him.” This is what I have said; He offered an example to our infirmity. He had not lost power, but He was comforting our weakness. For it would happen, as I have said, that some believer in Him would retreat into concealment, lest he should be found by the persecutors; and lest the concealment should be objected to him as a crime, that occurred first in the head, which should afterwards be confirmed in the member.
For it is said, “He would not walk in Judea, because the Jews sought to kill Him,” just as if Christ were not able both to walk among the Jews, and not be killed by them. For He manifested this power when He willed; for when they would lay hold of Him, as He was now about to suffer, “He said to them, Whom do you seek? They answered, Jesus. Then, said He, I am He,” not concealing, but manifesting Himself. That manifestation, however, they did not withstand, but “going backwards, they fell to the ground.” And yet, because He had come to suffer, they rose up, laid hold of Him, led Him away to the judge, and slew Him.
But what was it they did? That which a certain scripture says: “The earth was delivered into the hands of the ungodly.” The flesh was given into the power of the Jews; and this that thereby the bag, as it were, might be rent asunder, whence our purchase-price might run out.
Source: Tractates on the Gospel of John (New Advent)