Thomas Aquinas

“ And since the soul as long as it is a wayfarer is changeable in respect of the free-will, it results that grace is in the soul in a changeable manner. But an instrumental power follows rather the condition of the principal agent: and consequently a character exists in the soul in an indelible manner, not from any perfection of its own, but from the perfection of Christ's Priesthood, from which the character flows like an instrumental power. ”

“ Although a character is a reality and a sacrament, it does not follow that whatever is a reality and a sacrament, is also a character. With regard to the other sacraments we shall explain further on what is the reality and what is the sacrament. ”

“ Man is sanctified by each of the sacraments, since sanctity means immunity from sin, which is the effect of grace. But in a special way some sacraments, which imprint a character, bestow on man a certain consecration, thus deputing him to the Divine worship: just as inanimate things are said to be consecrated forasmuch as they are deputed to Divine worship. ”

“ The character imprinted on the soul is a kind of sign in so far as it is imprinted by a sensible sacrament: since we know that a certain one has received the baptismal character, through his being cleansed by the sensible water. Nevertheless from a kind of likeness, anything that assimilates one thing to another, or discriminates one thing from another, even though it be not sensible, can be called a character or a seal ”

“ In like manner the character of the faithful is that by which the faithful of Christ are distinguished from the servants of the devil, either in relation to eternal life, or in relation to the worship of the Church that now is. ”

“ Consequently, these three sacraments imprint a character, namely, Baptism, Confirmation, and order.
Reply to Objection 1: Every sacrament makes man of the a participator in Christ's Priesthood, from the fact that it confers on him some effect thereof. But every sacrament does not depute a man to do or receive something pertaining to the worship of the priesthood of Christ: while it is just this that is required for a sacrament to imprint a character. ”

“ And for both these purposes some power is needed; for to bestow something on others, active power is necessary; and in order to receive, we need a passive power. Consequently, a character signifies a certain spiritual power ordained unto things pertaining to the Divine worship. ”

“ Objection 3: Further, when the end ceases, the means to the end should cease also: thus after the resurrection there will be no marriage, because begetting will cease, which is the purpose of marriage. ”