Ex opere operato, by the working of the work itself, means that the sacrament is valid so long as matter, form, and intention are correct, regardless of the disposition of the minister (who must still be a validly ordained minister). What this means is that so long as you are using bread and wine of proper constitution, the proper ritual words given by the Church in the context of her liturgy, and intend to do what the Church does in the sacrament (i.e. confect the bread and wine into the Body and Blood of Christ), then the consecration occurs. Letâs say you have a priest who is in mortal sin or who does not believe any longer in the Eucharist or even in Godâby virtue of his using proper matter (bread and wine) and form (the ritual of the Church), his intention is presumed, even if it is not fully formed within him. In short, ex opere operato means that as long as all the other factors are presentâmatter, form, intent, and the validly ordained ministerâthe sacrament still occurs, even if the priestâs disposition is not complete or correct.
-ACEGC