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" (Lk. 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 (Jn. 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."
In regard to the whole community, man is perfected in two ways. First, by receiving power to rule the community and to exercise public acts: and corresponding to this in the spiritual life there is the sacrament of order, according to the saying of Heb. 7:27, that priests offer sacrifices not for themselves only, but also for the people. Secondly in regard to natural propagation. This is accomplished by Matrimony both in the corporal and in the spiritual life: since it is not only a sacrament but also a function of nature.
We may likewise gather the number of the sacraments from their being instituted as a remedy against the defect caused by sin. For Baptism is intended as a remedy against the absence of spiritual life; Confirmation, against the infirmity of soul found in those of recent birth; the Eucharist, against the soul's proneness to sin; Penance, against actual sin committed after baptism; Extreme Unction, against the remainders of sins---of those sins, namely, which are not sufficiently removed by Penance, whether through negligence or through ignorance; order, against divisions in the community; Matrimony, as a remedy against concupiscence in the individual, and against the decrease in numbers that results from death.
Some, again, gather the number of sacraments from a certain adaptation to the virtues and to the defects and penal effects resulting from sin. They say that Baptism corresponds to Faith, and is ordained as a remedy against original sin; Extreme Unction, to Hope, being ordained against venial sin; the Eucharist, to Charity, being ordained against the penal effect which is malice. order, to Prudence, being ordained against ignorance; Penance to Justice, being ordained against mortal sin; Matrimony, to Temperance, being ordained against concupiscence; Confirmation, to Fortitude, being ordained against infirmity.
ST 3. Q 16. A 1.