Reply Obj. 4: This argument proceeds on the ground of necessity. For thus Baptism, being of the greatest necessity, is the greatest of the sacraments, just as order and Confirmation have a certain excellence considered in their administration; and Matrimony by reason of its signification. For there is no reason why a thing should not be greater from a certain point of view which is not greater absolutely speaking. _______________________
FOURTH ARTICLE [III, Q. 65, Art. 4]
Whether All the Sacraments Are Necessary for Salvation?
Objection 1: It seems that all the sacraments are necessary for salvation. For what is not necessary seems to be superfluous. But no sacrament is superfluous, because "God does nothing without a purpose" (De Coelo et Mundo i). Therefore all the sacraments are necessary for salvation.
Obj. 2: Further, just as it is said of Baptism (John 3:5): "Unless a man be born again of water and the Holy Ghost, he cannot enter in to the kingdom of God," so of the Eucharist is it said (John 6:54): "Except you eat of the flesh of the Son of Man, and drink of His blood, you shall not have life in you." Therefore, just as Baptism is a necessary sacrament, so is the Eucharist.
Obj. 3: Further, a man can be saved without the sacrament of Baptism, provided that some unavoidable obstacle, and not his contempt for religion, debar him from the sacrament, as we shall state further on (Q. 68, A. 2). But contempt of religion in any sacrament is a hindrance to salvation. Therefore, in like manner, all the sacraments are necessary for salvation.
On the contrary, Children are saved by Baptism alone without the other sacraments.
I answer that, Necessity of end, of which we speak now, is twofold. First, a thing may be necessary so that without it the end cannot be attained; thus food is necessary for human life. And this is simple necessity of end. Secondly, a thing is said to be necessary, if, without it, the end cannot be attained so becomingly: thus a horse is necessary for a journey. But this is not simple necessity of end.
In the first way, three sacraments are necessary for salvation. Two of them are necessary to the individual; Baptism, simply and absolutely; Penance, in the case of mortal sin committed after Baptism; while the sacrament of order is necessary to the Church, since "where there is no governor the people shall fall" (Prov. 11:14).
But in the second way the other sacraments are necessary. For in a sense Confirmation perfects Baptism; Extreme Unction perfects Penance; while Matrimony, by multiplying them, preserves the numbers in the Church.