"But sometimes, whilst the mind is sustained with the plenitude and richness of a gift so large, if it enjoys uninterrupted security in these things, it forgets from what source it has them, and imagines that it derives from itself, which it sees to be never wanting to it. Hence it is that this same grace sometimes withdraws itself for our good, and shews the presumptuous mind how weak it is in itself. For then we really learn whence our good qualities proceed, when, by seemingly losing them, we are made sensible that they are never preserved by our own efforts. And so, for the purpose of tutoring us in humility, it very often happens that, when the crisis of temptation is upon us, such extreme folly comes down upon our wisdom, that the mind, being dismayed, knows nothing how to meet the evils that are threatened, or how to make ready against temptation."
Gregory the Great, Morals in Job, II.78.