Ex opere operato is a Latin expression meaning “by the work worked,” or “from the work of the work itself.”
It refers to the fact that the sacraments confer grace when the sign is validly affected—not as the result of activity on the part of the minister or recipient but by the power and promise of God.
Now, to receive the fruits of the sacraments, the recipient should be properly disposed with the intention of receiving the sacrament. This means reception of grace via the sacraments is not automatic.
But the ex opere operato nature of the sacraments reminds us that, while a proper disposition is necessary to receive grace in the sacraments, it isn’t the cause of that grace. The correct use of the sign instituted by Christ produces the grace irrespective of the merits of either minister or recipient. (8:11)