Their faith alone will not profit them, because they have not done works of righteousness. - Pelagius

Under the plea that it is impossible not to sin, they are given a false sense of security in sinning ... Anyone who hears that it is not possible for him to be without sin will not even try to be what he judges to be impossible, and the man who does not try to be without sin must perforce sin all the time, and all the more boldly because he enjoys the false security of believing that it is impossible for him not to sin ... But if he were to hear that he is able not to sin, then he would have exerted himself to fulfil what he now knows to be possible when he is striving to fulfil it, to achieve his purpose for the most part, even if not entirely.

It was because God wished to bestow on the rational creature the gift of doing good of his own free will and the capacity to exercise free choice, by implanting in man the possibility of choosing either alternative. ... He could not claim to possess the good of his own volition, unless he was the kind of creature that could also have possessed evil. Our most excellent creator wished us to be able to do either but actually to do only one, that is, good, which he also commanded, giving us the capacity to do evil only so that we might do His will by exercising our own. That being so, this very capacity to do evil is also good – good, I say, because it makes the good part better by making it voluntary and independent, not bound by necessity but free to decide for itself.

When will a man guilty of any crime or sin accept with a tranquil mind that his wickedness is a product of his own will, not of necessity, and allow what he now strives to attribute to nature to be ascribed to his own free choice? It affords endless comfort to transgressors of the divine law if they are able to believe that their failure to do something is due to inability rather than disinclination, since they understand from their natural wisdom that no one can be judged for failing to do the impossible and that what is justifiable on grounds of impossibility is either a small sin or none at all.