How, although the thing may be necessary, God may not do it by a compulsory necessity; and what is the nature of that necessity which removes or lessens gratitude, and what necessity increases it.
Boso. But if it be so, then God seems as it were compelled, for the sake of avoiding what is unbecoming 243, to secure the salvation of man. How, then, can it be denied that he does it more on his own account than on ours? But if it be so, what thanks do we owe him for what he does for himself? How shall we attribute our salvation to his grace, if he saves us from necessity?
Anselm. There is a necessity which takes away or lessens our gratitude to a benefactor, and there is also a necessity by which the favor deserves still greater thanks. For when one does a benefit from a necessity to which he is unwillingly subjected, less thanks are due him, or none at all. But when he freely places himself under the necessity of benefiting another, and sustains that necessity without reluctance, then he certainly deserves greater thanks for the favor. For this should not be called necessity but grace, inasmuch as he undertook or maintains it, not with any constraint, but freely. For if that which to-day you promise of your own accord you will give to-morrow, you do give to-morrow with the same willingness; though it be necessary for you, if possible, to redeem your promise, or make yourself a liar; notwithstanding, the recipient of your favor is as much indebted for your precious gift as if you had not promised it, for you were not obliged to make yourself his debtor before the time of giving it: just so is it when one undertakes, by a vow, a design of holy living. For though after his vow he ought necessarily to perform, lest he suffer the judgment of an apostate, and, although he may be compelled to keep it even unwillingly, yet, if he keep his vow cheerfully, he is not less but more pleasing to God than if he had not vowed. For he has not only given up the life of the world, but also his personal liberty, for the sake of God; and 244he cannot be said to live a holy life of necessity, but with the same freedom with which he took the vow. Much more, therefore, do we owe all thanks to God for completing his intended favor to man; though, indeed, it would not be proper for him to fail in his good design, because wanting nothing in himself he begun it for our sake and not his own. For what man was about to do was not hidden from God at his creation; and yet by freely creating man, God as it were bound himself to complete the good which he had begun. In fine, God does nothing by necessity, since he is not compelled or restrained in anything. And when we say that God does anything to avoid dishonor, which he certainly does not fear, we must mean that God does this from the necessity of maintaining his honor; which necessity is after all no more than this, viz., the immutability of his honor, which belongs to him in himself, and is not derived from another; and therefore it is not properly called necessity. Yet we may say, although the whole work which God does for man is of grace, that it is necessary for God, on account of his unchangeable goodness, to complete the work which he has begun.
Boso. I grant it.
Source: Cur Deus Homo (CCEL)