The text Widor chose for this anthem is the last two verses of the hymn Pange lingua, which have often been used alone, especially as a part of the service of Benediction of the Blessed Sacrament. The hymn was written by Thomas Aquinas for the feast of Corpus Christi. Here is the text of the whole hymn, in my own translation...not necessarily good poetry, but I want to convey the literal text as carefully as I can.
Sing, O tongue, the mystery of the glorious body and the precious blood, which, to redeem the world, the fruit of a noble womb, the King of the nations, poured out.
Given for us, born to us, from an intact Virgin, and dwelling in the world, after the seed of the word was sown, he closed the times of his dwelling in a wondrous way.
In the night of the final supper, lying with his brothers, after fully observing the Law of the right foods, he gives himself with his own hands as food to the crowd of twelve.
The word made flesh makes true bread into flesh by a word: and pure wine he makes into the blood of Christ, and if the senses fail, faith alone suffices to strengthen a sincere heart.
So therefore we worship the Sacrament with a bow, and the ancient lesson gives way to a new rite: let faith supply a supplement to the failing of senses.
To the begetter and the begotten, praise and rejoicing, salvation, honor, and virtue let there be, and blessing: to the one proceeding from each be equal praise. Amen.
What we sung on Sunday was then the last two verses of this. The title, tantum ergo, translates "So therefore."
What to make of these words? We are asked that faith should supply what is lacking to our senses. The deeper reality which underlies what we see lies hidden, but hidden only to the body's limited sensing. To the eyes of faith, we can see what cannot be seen. Just as we know the sacrament to be the Body of Christ, just as we know Jesus to have been the Word made flesh, so around us every day is more of the same. In the eye of our beloved we see love looking back at us, but the eye which sees is the eye of loving trust: to the stranger this is hidden.
Aquinas plays delightfully on the sense of interchange and exchange here in the fourth verse. The word made flesh makes true bread into flesh by a word. The divine word at creation, the word spoken over the waters, the word let there be light becomes flesh in Jesus, becomes a human, subject to the frailty of human nature. And just so, the word of Christ in turn makes mere bread into the Body of Christ given for the world, the sacrament of grace and redemption.
And so the fifth verse captures this sense of exchange, in which the setting of the ancient Passover becomes the context for the new heavenly banquet, one exchanges for the other. Even the invocation of the Trinity in the last verse captures the same exchange and interchange. Begetter and begotten receive praise, the Father and the Son, but here we think of the mutual relation between them. The one who gives and the one who receives, the one which turns and the one which is turned. And the Holy Spirit again is described as the one who proceeds from each, defined again in terms of the relationship between them.
It is this mutual indwelling of the Persons of the Trinity into which we are drawn up by Christ dwelling within us, and it is by means of the sacraments that Christ dwells within us. Become what you eat, receive what you are, said Saint Augustine.
