Secondly, this is made clear by considering the relation of the sacraments to one another. For all the other sacraments seem to be ordained to this one as to their end. For it is manifest that the sacrament of order is ordained to the consecration of the Eucharist: and the sacrament of Baptism to the reception of the Eucharist: while a man is perfected by Confirmation, so as not to fear to abstain from this sacrament. By Penance and Extreme Unction man is prepared to receive the Body of Christ worthily. And Matrimony at least in its signification, touches this sacrament; in so far as it signifies the union of Christ with the Church, of which union the Eucharist is a figure: hence the Apostle says ( Eph. 5:32 ): "This is a great sacrament: but I speak in Christ and in the Church."
Thirdly, this is made clear by considering the rites of the sacraments. For nearly all the sacraments terminate in the Eucharist, as Dionysius says (Eccl. Hier. iii): thus those who have been ordained receive Holy Communion, as also do those who have been baptized, if they be adults.
The remaining sacraments may be compared to one another in several ways. For on the ground of necessity, Baptism is the greatest of the sacraments; while from the point of view of perfection, order comes first; while Confirmation holds a middle place. The sacraments of Penance and Extreme Unction are on a degree inferior to those mentioned above; because, as stated above (A[2]), they are ordained to the Christian life, not directly, but accidentally, as it were, that is to say, as remedies against supervening defects. And among these, Extreme Unction is compared to Penance, as Confirmation to Baptism; in such a way, that Penance is more necessary, whereas Extreme Unction is more perfect.
Reply to Objection 1: Matrimony is ordained to the common good as regards the body. But the common spiritual good of the whole Church is contained substantially in the sacrament itself of the Eucharist.
Reply to Objection 2: By order and Confirmation the faithful of Christ are deputed to certain special duties; and this can be done by the prince alone. Consequently the conferring of these sacraments belongs exclusively to a bishop, who is, as it were, a prince in the Church. But a man is not deputed to any duty by the sacrament of the Eucharist, rather is this sacrament the end of all duties, as stated above.
Reply to Objection 3: The sacramental character, as stated above (Q[63], A[3]), is a kind of participation in Christ's priesthood. Wherefore the sacrament that unites man to Christ Himself, is greater than a sacrament that imprints Christ's character.
Reply to Objection 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.
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.
Objection 2: Further, just as it is said of Baptism ( Jn. 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 ( Jn. 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.
Objection 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.
Reply to Objection 1: For a thing not to be superfluous it is enough if it be necessary either in the first or the second way. It is thus that the sacraments are necessary, as stated above.
Reply to Objection 2: These words of our Lord are to be understood of spiritual, and not of merely sacramental, eating, as Augustine explains (Tract. xxvi super Joan.).
Reply to Objection 3: Although contempt of any of the sacraments is a hindrance to salvation, yet it does not amount to contempt of the sacrament, if anyone does not trouble to receive a sacrament that is not necessary for salvation. Else those who do not receive orders, and those who do not contract Matrimony, would be guilty of contempt of those sacraments.