Thomas Aquinas

“ Of those things that are done after Baptism in respect of the person baptized, something is done which is not a mere sign, but produces an effect, for instance, the anointing on the top of the head, the effect of which is the preservation of baptismal grace. And there is something which has no effect, but is a mere sign, for instance, the baptized are given a white garment to signify the newness of life. ”

“ He who answers in the child's stead: "I do believe," does not foretell that the child will believe when it comes to the right age, else he would say: "He will believe"; but in the child's stead he professes the Church's faith which is communicated to that child, the sacrament of which faith is bestowed on it, and to which faith he is bound by another. For there is nothing unfitting in a person being bound by another in things necessary for salvation. ”

“ But those things that are done in the exorcism remove the twofold impediment against the reception of saving grace. Of these, one is the outward impediment, so far as the demons strive to hinder man's salvation. And this impediment is removed by the breathings, whereby the demon's power is cast out, as appears from the passage quoted from Augustine, i.e. as to the devil not placing obstacles against the reception of the sacrament. Nevertheless, the demon's power over man remains as to the stain of sin, and the debt of punishment, until sin be washed away by Baptism. ”

“ Further, a man, when catechized, confesses his faith. Now a child cannot confess its faith by itself, nor can anyone else in its stead; both because no one can bind another to do anything; and because one cannot know whether the child, having come to the right age, will give its assent to faith. ”

“ Whether children or young people approach the sacrament of regeneration, they should not come to the fount of life before the unclean spirit has been expelled from them by the exorcisms and breathings of the clerics. ”

“ To readers and exorcists belongs the duty of catechizing and exorcizing, not, indeed, principally, but as ministers of the priest in these things.
Reply to Objection 3: Instruction is manifold. One leads to the embracing of the Faith; and is ascribed by Dionysius to bishops (Eccl. Hier. ii) and can be undertaken by any preacher, or even by any believer. Another is that by which a man is taught the rudiments of faith, and how to comport himself in receiving the sacraments: this belongs secondarily to the ministers, primarily to the priests. ”

“ Holy water is used against the assaults of demons from without. But exorcisms are directed against those assaults of the demons which are from within. hence those who are exorcized are called energumens, as it were "laboring inwardly." ”