Obj. 2: Further, a sacrament is intended as a remedy for the defect caused by sin. Now this is twofold, punishment and guilt. Therefore two sacraments would be enough.
Obj. 3: Further, sacraments belong to the actions of the ecclesiastical hierarchy, as Dionysius explains (Eccl. Hier. v). But, as he says, there are three actions of the ecclesiastical hierarchy, namely, "to cleanse, to enlighten, to perfect." Therefore there should be no more than three sacraments.
Obj. 4: Further, Augustine says (Contra Faust. xix) that the "sacraments" of the New Law are "less numerous" than those of the Old Law. But in the Old Law there was no sacrament corresponding to Confirmation and Extreme Unction. Therefore these should not be counted among the sacraments of the New Law.
Obj. 5: Further, lust is not more grievous than other sins, as we have made clear in the Second Part (I-II, Q. 74, A. 5; II-II, Q. 154, A. 3). But there is no sacrament instituted as a remedy for other sins. Therefore neither should matrimony be instituted as a remedy for lust.
Obj. 6: On the other hand, It seems that there should be more than seven sacraments. For sacraments are a kind of sacred sign. But in the Church there are many sanctifications by sensible signs, such as Holy Water the Consecration of Altars, and such like. Therefore there are more than seven sacraments.
Obj. 7: Further, Hugh of St. Victor (De Sacram. i) says that the sacraments of the Old Law were oblations, tithes and sacrifices. But the Sacrifice of the Church is one sacrament, called the Eucharist. Therefore oblations also and tithes should be called sacraments.
Obj. 8: Further, there are three kinds of sin, original, mortal and venial. Now Baptism is intended as a remedy against original sin, and Penance against mortal sin. Therefore besides the seven sacraments, there should be another against venial sin.
I answer that, As stated above (Q. 62, A. 5; Q. 63, A. 1), the sacraments of the Church were instituted for a twofold purpose: namely, in order to perfect man in things pertaining to the worship of God according to the religion of Christian life, and to be a remedy against the defects caused by sin. And in either way it is becoming that there should be seven sacraments.
For spiritual life has a certain conformity with the life of the body: just as other corporeal things have a certain likeness to things spiritual. Now a man attains perfection in the corporeal life in two ways: first, in regard to his own person; secondly, in regard to the whole community of the society in which he lives, for man is by nature a social animal. With regard to himself man is perfected in the life of the body, in two ways; first, directly (per se), i.e. by acquiring some vital perfection; secondly, indirectly (per accidens), i.e. by the removal of hindrances to life, such as ailments, or the like. Now the life of the body is perfected directly, in three ways. First, by generation whereby a man begins to be and to live: and corresponding to this in the spiritual life there is Baptism, which is a spiritual regeneration, according to Titus 3:5: "By the laver of regeneration," etc. Secondly, by growth whereby a man is brought to perfect size and strength: and corresponding to this in the spiritual life there is Confirmation, in which the Holy Ghost is given to strengthen us. Wherefore the disciples who were already baptized were bidden thus: "Stay you in the city till you be endued with power from on high" (Luke 24:49). Thirdly, by nourishment, whereby life and strength are preserved to man; and corresponding to this in the spiritual life there is the Eucharist. Wherefore it is said (John 6:54): "Except you eat of the flesh of the Son of Man, and drink His blood, you shall not have life in you."
And this would be enough for man if he had an impassible life, both corporally and spiritually; but since man is liable at times to both corporal and spiritual infirmity, i.e. sin, hence man needs a cure from his infirmity; which cure is twofold. One is the healing, that restores health: and corresponding to this in the spiritual life there is Penance, according to Ps. 40:5: "Heal my soul, for I have sinned against Thee." The other is the restoration of former vigor by means of suitable diet and exercise: and corresponding to this in the spiritual life there is Extreme Unction, which removes the remainder of sin, and prepares man for final glory. Wherefore it is written (James 5:15): "And if he be in sins they shall be forgiven him."