But these cavillers seem to be ignorant of the nature of necessity. For there is a twofold necessity: a necessity of constraint, and this diminishes the praiseworthiness of virtuous acts, as telling against their voluntariness: for that is done under constraint, which is contrary to the will. There is again a necessity springing out of interior inclination; and this, far from diminishing, increases the credit of a virtuous act: for it makes the will tend to the act of virtue all the more earnestly. For evidently, the more perfect the habit of virtue is, with all the more force does it urge the will to the act of virtue and leaves it less chance of swerving. Nay, if it attains to the highest pitch of perfection, it induces a sort of necessity of well- doing, as will appear in the case of the Blessed, who cannot sin (B. IV, Chap. XCII); nor yet is there anything thereby lost either to the freedom of the wilt or to the goodness of the act. There is another necessity derived from the bearing of the means on the end in view, as when it is said to be necessary for one to find a ship in order to cross the sea. But neither does this necessity diminish the freedom of the will or the goodness of the acts: nay rather, for one to act as doing something necessary to an end is in itself praiseworthy, and all the more praiseworthy the better the end. But it will be seen that the necessity of observing what one has vowed to observe, or obeying the superior under whom one has placed oneself, is not a necessity of constraint: nor again is it a necessity arising out of interior inclination, but out of the bearing of means on the end: for it is necessary for the votary to do this or that, if the vow is to be fulfilled, or the obedience kept. Since then these are praiseworthy ends, inasmuch as they are acts whereby a man submits himself to God, the aforesaid necessity takes off nothing from the praise of virtue.
From yet another point of view the fulfilment of a vow, or of a superior's commands, for God's sake, is worthy of greater praise or reward. For as one act may be an act of two vices, in that the act of one vice is directed to the end of another vice, e.g., when one steals to commit fornication, in which case the act is specifically one of avarice, but intentionally one of lust,* -- so in the same way the act of one virtue may be directed to the act of another virtue, as when one gives for charity, in which case the act is specifically one of liberality, but finally one of charity: such an act is more praiseworthy for the greater virtue of charity than for liberality: hence, though the liberality come to fall short, the act will be more praiseworthy, inasmuch as it is referred to charity, and worthy of greater reward, than if it were done with greater liberality, but not in view of charity.* Let us suppose then a man doing some act of virtue, say, fasting, or restraining his sexual passion: if he does this without a vow, it will be an act of chastity, or abstinence: but if he does it under a vow, it is further referable to another virtue, that virtue to which it belongs to vow and pay one's vows to God, which is called the virtue of religion, a higher virtue than chastity, or abstinence, as putting us in a right relation with God. The act of abstinence therefore, or continence, will be more praiseworthy inasmuch as it is done under vow, even though the doer of it does not take so much delight in his abstinence, or continence: that deficiency is made up by his taking delight in a higher virtue, which is religion.
If any one does anything for God, he offers the act to God, such as it is: but if he does it under a vow, he offers to God not only the act but also the power: thus he clearly has the intention of rendering to God some greater service. Therefore his act will be the more virtuous by reason of the greater good intended, even though another shows himself more fervent in the execution.
Moreover, the will that goes before a deed, virtually endures throughout the whole course of the doing of it; and renders it praiseworthy, even when the agent in the execution of his work is not thinking of the purpose for which he began: for it is not necessary for him who has undertaken a journey for God's sake, to be actually thinking of God at every step of the journey. But clearly he who has vowed to do a thing has willed it more intensely than another who simply has a purpose of doing it; because he has not only willed to do it, but also has willed to fortify himself against failing to do it. This original earnestness of will renders the fulfilment of the vow, with more or less of earnestness, praiseworthy, even when the will is not actually fixed on the work, or is fixed on it but languidly. Thus what is done under vow is more praiseworthy than what is done without vow, other conditions however being equal.*
3.137 : Arguments against Perpetual Continence, with Replies
3.140 : That neither all Good Works nor all Sins are Equal