virtue is the better and more meritorious for being
commanded by a superior virtue, whose act it becomes through being
commanded by it, just as the act of faith or hope is better if it be
commanded by charity. Hence the works of the other moral virtues (for
instance, fasting, which is an act of abstinence; and being
continent, which is an act of chastity) are better and more
meritorious, if they be done in fulfilment of a vow, since thus they
belong to the divine worship, being like sacrifices to God. Wherefore
Augustine says (De Virg. viii) that "not even is virginity honorable
as such, but only when it is consecrated to God, and cherished by
godly continence."

Secondly, because he that vows something and does it, subjects
himself to God more than he that only does it; for he subjects
himself to God not only as to the act, but also as to the power,
since in future he cannot do something else. Even so he gives more
who gives the tree with its fruit, than he that gives the fruit only,
as Anselm [*Eadmer] observes (De Simil. viii). For this reason, we
thank even those who promise, as stated above (A. 5, ad 2).

Thirdly, because a vow fixes the will on the good immovably and to do
anything of a will that is fixed on the good belongs to the
perfection of virtue, according to the Philosopher (Ethic. ii, 4),
just as to sin with an obstinate mind aggravates the sin, and is
called a sin against the Holy Ghost, as stated above (Q. 14, A. 2).

Reply Obj. 1: The passage quoted should be understood as referring to
necessity of coercion which causes an act to be involuntary and
excludes devotion. Hence he says pointedly: "Lest that which we are
free to do be done without devotion and unwillingly." On the other
hand the necessity resulting from a vow is caused by the immobility
of the will, wherefore it strengthens the will and increases
devotion. Hence the argument does not conclude.

Reply Obj. 2: According to the Philosopher, necessity of coercion, in
so far as it is opposed to the will, causes sorrow. But the necessity
resulting from a vow, in those who are well disposed, in so far as it
strengthens the will, causes not sorrow but joy. Hence Augustine says
(Ep. ad Arment. et Paulin. cxxcii): "Repent not of thy vow: thou
shouldst rather rejoice that thou canst no longer do what thou
mightest lawfully have done to thy detriment." If, however, the very
deed, considered in itself, were to become disagreeable and
involuntary aft