From Parochial and Plain Sermons
by Venerable John Henry Newman:

In an earlier part of His ministry, the same question had been asked, and the same answer given under a different image. The Jews "said unto Him, What sign showest Thou unto us, seeing that Thou doest these things?" He in like manner answers; "Destroy this temple, and in three days I will raise it up." [John ii. 19.] They misunderstood Him, and He did not set them right. For they were to see, and see not; they were not to witness the Sign then, nor were they allowed to apprehend His language now. He spoke of the resurrection of His body, and they were not at that season to see Him whom they had pierced.

Now what is remarkable in this passage is this, that our Lord promised a great sign parallel to those wrought by the old prophets; yet instead of being public as theirs was, it was in the event, like Jonah's, a secret sign. Few saw it; it was to be received by all, but on faith; it was addressed to the humble and lowly. When it took place, and St. Thomas refused to believe without sight, our Lord said to him, "Thomas, because thou hast seen Me, thou hast believed; blessed are they that have not seen, and yet have believed." The Apostle, perhaps, might have been arguing, "If this be the Lord's great Sign, surely it is to be seen. What is meant by the resurrection but an evidence which is to be addressed to my senses? I have to believe, and this is to assure my belief." Yet St. Thomas would have been more blessed, had he believed Christ's miraculous Presence without seeing it; and our Lord implied that such persons there would be.