18. Let us look next at the passage: “So, then, it is not of him that willeth, nor of him that runneth, but of God that showeth mercy.”[535] For they who find fault say: If “it is not of him that willeth, nor of him that runneth, but of God that showeth mercy,” salvation does not depend upon ourselves, but upon the arrangement[536] made by Him who has formed[537] us such as we are, or on the purpose[538] of Him who showeth mercy when He pleases. Now we must ask these persons the following questions: Whether to desire what is good is virtuous or vicious; and whether the desire to run in order to reach the goal in the pursuit of what is good be worthy of praise or censure? And if they shall say that it is worthy of censure, they will return an absurd answer;[539] since the saints desire and run, and manifestly in so acting do nothing that is blameworthy. But if they shall say that it is virtuous to desire what is good, and to run after what is good, we shall ask them how a perishing nature desires better things;[540] for it is like an evil tree producing good fruit, since it is a virtuous act to desire better things. They will give [perhaps] a third answer, that to desire and run after what is good is one of those things that are indifferent,[541] and neither beautiful[542] nor wicked. Now to this we must say, that if to desire and to run after what is good be a thing of indifference, then the opposite also is a thing of indifference, viz. to desire what is evil, and to run after it. But it is not a thing of indifference to desire what is evil, and to run after it. And therefore also, to desire what is good, and to run after it, is not a thing of indifference. Such, then, is the defence which I think we can offer to the statement, that “it is not of him that willeth, nor of him that runneth, but of God that showeth mercy.”[543] Solomon says in the book of Psalms (for the song of Degrees[544] is his, from which we shall quote the words): “Unless the Lord build the house, they labour in vain that build it; except the Lord keep the city, the watchman waketh in vain:”[545] not dissuading us from building, nor teaching us not to keep watch in order to guard the city in our soul, but showing that what is built without God, and does not receive a guard from Him, is built in vain and watched to no purpose, because God might reasonably be entitled the Lord of the building; and the Governor of all things, the Ruler of the guard of the city. As, then, if we were to say that such a building is not the work of the builder, but of God, and that it was not owing to the successful effort of the watcher, but of the God who is over all, that such a city suffered no injury from its enemies, we should not be wrong,[546] it being understood that something also had been done by human means, but the benefit being gratefully referred to God who brought it to pass; so, seeing that the [mere] human desire is not sufficient to attain the end,