3 He proceeds: “And I am glorified in them.” He now speaks of His glorification as already accomplished, although it was still future; while a little before He was demanding of the Father its accomplishment. But whether this be the same glorification, whereof He had said, “And now, O Father, glorify Thou me with Your own self with the glory which I had with You before the world was,” is certainly a point worthy of examination. For if “with You,” how can it be “in them”? Is it when this very knowledge is imparted to them, and, through them, to all who believe them as His witnesses? In such a way we may clearly understand Christ as having said of the apostles, that He was glorified in them; for in saying that it was already accomplished, He showed that it was already foreordained, and only wished what was future to be regarded as certain.
Source: Tractates on the Gospel of John (New Advent)