Chapter 10 [VI.]—The Gift of Perseverance Can Be Obtained by Prayer.
But you write that “these brethren will not have this perseverance so preached as that it cannot be obtained by prayer or lost by obstinacy.” 3578 In this they are little careful in considering what they say. For we are speaking of that perseverance whereby one perseveres unto the end, and if this is given, one does persevere unto the end; but if one does not persevere unto the end, it is not given, which I have already sufficiently discussed above. Let not men say, then, that perseverance is given to any one to the end, except when the end itself has come, and he to whom it has been given has been found to have persevered unto the end. Certainly, we say that one whom we have known to be chaste is chaste, whether he should continue or not in the same chastity; and if he should have any other divine endowment which may be kept and lost, we say that he has it as long as he has it; and if he should lose it, we say that he had it. But since no one has perseverance to the end except he who does persevere to the end, many people may have it, but none can lose it. For it is not to be feared that perchance when a man has persevered unto the end, some evil will may arise in him, so that he does not persevere unto the end. This gift of God, therefore, may be obtained by prayer, but when it has been given, it cannot be lost by contumacy. For when any one has persevered unto the end, he neither can lose this gift, nor others which he could lose before the end. How, then, can that be lost, whereby it is brought about that even that which could be lost is not lost?
Hilarys Letter in Augustins Letters, 226, ch. 3.