Glossa Ordinaria

(ap. Anselm.) This power was committed specially to Peter, that we might thereby be invited to unity. For He therefore appointed him the head of the Apostles, that the Church might have one principal Vicar of Christ, to whom the different members of the Church should have recourse, if ever they should have dissensions among them. But if there were many heads in the Church, the bond of unity would be broken. Some say that the words upon earth denote that power was not given to men to bind and loose the dead, but the living; for he who should loose the dead would do this not upon earth, but after the earth.