Pange Lingua Gloriosi Corporis Mysterium is a hymn written by St Thomas Aquino (1225?1274) for the Feast of Corpus Christi . It is also sung on Maundy Thursday, during the procession from the church to the place where the Blessed Sacrament is kept until Good Friday. The last two stanzas, called separately Tantum Ergo, are sung at Benediction of the Blessed Sacrament. The hymn expresses the doctrine of transubstantiation, in which, according to the Roman Catholic faith, the bread and wine are changed into the Body and Blood of Christ.