Indeed it is greater even than the power of the Virgin Mary. While the Blessed Virgin was the human agency by which Christ became incarnate a single time, the priest brings Christ down from heaven, and renders Him present on our altar as the eternal Victim for the sins of man, not once but a thousand times! The priest speaks and lo! Christ, the eternal and omnipotent God, bows his head in humble obedience to the priest’s command.
Of what sublime dignity is the office of the Christian priest who is thus privileged to act as the ambassador and the vice-gerent of Christ on earth! He continues the essential ministry of Christ: he teaches the faithful with the authority of Christ, he pardons the penitent sinner with the power of Christ, he offers up again the same sacrifice of adoration and atonement which Christ offered on Calvary. No wonder that the name which spiritual writers are especially fond of applying to the priest is that of alter Christus. For the priest is and should be another Christ."
John A. O'Brien, The Faith of Millions: The Credentials of the Catholic Religion, p. 255-256