The hymn sung as the Blessed Sacrament is placed on the altar.
The last two verses of a longer hymn Saint Thomas Aquinas wrote for Corpus Christi, now sung at the exposition of the Blessed Sacrament.
When: At the beginning of Benediction, as the monstrance is placed on the altar.
Why: It names what is on the altar: the victim of the Cross, the same one, still opening heaven. Everything else at Benediction follows from that claim.
O saving Victim, opening wide the gate of heaven to us below, our foes press hard on every side; thine aid supply, thy strength bestow.
To thy great name be endless praise, immortal Godhead, One in Three. Oh, grant us endless length of days in our true native land with thee. Amen.