A Priest commits a grave sin of sacrilege if he celebrates Mass whilst he himself is in a state of mortal sin. But that would not render the consecration invalid. The words of consecration have their effect quite apart from the state of the celebrant’s soul. He consecrates in virtue of his priesthood, not in virtue of his being in a state of grace or of sin. It is his loss if he be not in God’s grace, but the communicant suffers no loss in receiving Communion from his hands. It is the priesthood of Christ in him that consecrates, and that is not less efficacious because a Priest sins personally.
Radio Replies Volume 1 by Rev. Dr. Leslie Rumble MSC and Rev. Charles Mortimer Carty