Thomas Aquinas

“ Wicked men do not owe their power of conferring sacraments to their being members of the devil. Consequently, it does not follow that "a fortiori" the devil, their head, can do so.
Art. 8 - Whether the minister's intention is required for the validity of a sacrament? Objection 1: It seems that the minister's intention is not required for the validity of a sacrament. For the minister of a sacrament works instrumentally. But the perfection of an action does not depend on the intention of the instrument, but on that of the principal agent. ”

“ Now it is possible for a man to work with a lifeless instrument, and separated from him as to bodily union, provided it be united to him by some sort of motion: for a workman works in one way with his hand, in another with his axe. Consequently, it is thus that Christ works in the sacraments, both by wicked men as lifeless instruments, and by good men as living instruments. ”

“ Therefore it seems that the sacramental effect is the work not only of God, but also of the ministers of the Church.
Objection 2: Further, certain prayers are offered up in conferring the sacraments. But the prayers of the righteous are more acceptable to God than those of any other, according to Jn. 9:31: "If a man be a server of God, and doth His will, him He heareth." Therefore it stems that a man obtains a greater sacramental effect if he receive it from a good minister. Consequently, the interior effect is partly the work of the minister and not of God alone. ”

“ The other was the power of "excellence," which belongs to Him as man. This power He could communicate to ministers; namely, by giving them such a fulness of grace---that their merits would conduce to the sacramental effect---that by the invocation of their names, the sacraments would be sanctified---and that they themselves might institute sacraments, and by their mere will confer the sacramental effect without observing the sacramental rite. ”

“ And though they are not all handed down by the Scriptures, yet the Church holds them from the intimate tradition of the apostles, according to the saying of the Apostle (1 Cor. 11:34) : "The rest I will set in order when I come."
Reply to Objection 2: From their very nature sensible things have a certain aptitude for the signifying of spiritual effects: but this aptitude is fixed by the Divine institution to some special signification. This is what Hugh of St. Victor means by saying (De Sacram. i) that "a sacrament owes its signification to its institution." ”

“ This might be true enough of the ultimate effect, i.e. justification from sins; but as to that effect which is both real and sacramental, viz. the character, it does not appear possible for it to be made good by the devotion of the recipient, since a character is never imprinted save by a sacrament. ”

“ For a united instrument, the more powerful it is, is all the more able to lend its power to the separated instrument; as the hand can to a stick.
Reply to Objection 1: It was not through jealousy that Christ refrained from communicating to ministers His power of excellence, but for the good of the faithful; lest they should put their trust in men, and lest there should be various kinds of sacraments, giving rise to division in the Church ”

“ What men do in a less perfect manner, i.e. by sensible sacraments, which are proportionate to their nature, angels also do, as ministers of a higher degree, in a more perfect manner, i.e. invisibly---by cleansing, enlightening, and perfecting. ”

“ And he says in the epistle to Demophilus: "It seems presumptuous for such a man," i.e. a sinner, "to lay hands on priestly things; he is neither afraid nor ashamed, all unworthy that he is, to take part in Divine things, with the thought that God does not see what he sees in himself: he thinks, by false pretenses, to cheat Him Whom he calls his Father ”