What is the glass as used in other places in the NT?

Face to face - in James 1, we see ourselves, see our face reflected back to us. In 2 Corinthians 3:18, we see Christ reflected in all of Scripture. In this passage, we see the OT opened up to our understanding, and see Jesus face to face in the Scriptures - rather than having the OT veiled to us, now we see Him face to face.

Please see my response on page 1 of this thread for a look at the words used in this passage - of which I have not seen anyone address (except for this phrase here).