10 “Then said the Jews,” not to Him, but “to themselves, Whither will this man go, that we shall not find him? will he go unto the dispersion among the Gentiles, and teach the Gentiles?” For they knew not what they said; but, it being His will, they prophesied. The Lord was indeed about to go to the Gentiles, not by His bodily presence, but still with His feet. What were His feet? Those which Saul desired to trample upon by persecution, when the Head cried out to him, “Saul, Saul, why do you persecute me?” What is this saying that He said, “You shall seek me, and shall not find me: and where I am, there ye cannot come?”
Wherefore the Lord said this they knew not, and yet they did predict something that was to be without knowing it. For this is what the Lord said that they knew not the place, if place however it must be called, which is the bosom of the Father, from which Christ never departed; nor were they competent to conceive where Christ was, whence Christ never withdrew, whither He was to return, where He was all the while dwelling. How was it possible for the human heart to conceive this, least of all to explain it with the tongue?
This, then, they in no wise understood; and yet by occasion of this they foretold our salvation, that the Lord would go to the dispersion of the Gentiles, and would fulfill that which they read but did not understand. “A people whom I have not known served me, and by the hearing of the ear obeyed me.” They before whose eyes He was, heard Him not; those heard Him in whose ears He was sounded.
Source: Tractates on the Gospel of John (New Advent)