8 Let us begin, then, with hearing His exposition of what we have heard Him propounding. “Then said Jesus unto them again, Verily, verily, I say unto you, I am the door of the sheep.” See, He has opened the very door which was shut in His former description. He Himself is the door. We have come to know it; let us enter, or rejoice that we are already within. “All that ever came are thieves and robbers.” What is this, Lord, “All that ever came”? How so have You not come?
But understand; I said, “All that ever came,” meaning, of course, exclusive of myself. Let us recollect then. Before His coming came the prophets: were they thieves and robbers? God forbid. They did not come apart from Him, for they came with Him. When about to come, He sent heralds, but retained possession of the hearts of His messengers. Do you wish to know that they came with Him, who is Himself ever existent? Certainly He assumed human flesh at the time appointed. But what means that “ever”?
“In the beginning was the Word.” With Him, therefore, came those who came with the word of God. “I am,” said He, “the way, and the truth, and the life.” If He is the truth, with Him came those who were truthful. As many, therefore, as were apart from Him, were “thieves and robbers,” that is, had come to steal and to destroy.
Source: Tractates on the Gospel of John (New Advent)