Claves Regni, an online magazine, observed that verses 3,4, and 5 of the original hymn (which had eleven verses, reprinted in their entirety here) were omitted from most hymnbooks because of their references to the Te Deum, an ancient hymn attributed to St. Ambrose. (For lyrics in English and Latin, click here.)
My very favorite verse (which again I sing with far more conviction as a Catholic than ever I did before, and which is especially appropriate today) is verse six:
Today, as we remember our spiritual mothers and fathers who precede us to heaven, and who are there even now praying for us, let us never forget that "blest communion" that holds us close to the Sacred Heart.
O blest communion, fellowship divine!
We feebly struggle, they in glory shine;
Yet all are one in Thee, for all are Thine:
From Great Hymns of the Faith, 508