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… - 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.

Love of wealth is insatiable, desire for honour knows no fulfilment; possessions destined to meet with a speedy end are sought endlessly. But divine wisdom, heavenly riches, immortal honours we neglect in our indifference and sloth, and, as for spiritual riches, either we do not touch them at all or, if we get a slight taste of them, we at once suppose that we have had enough. The divine Wisdom invites us to its feasts in quite different terms: Those who eat me, she says, will hunger for more, and those who drink me will thirst for more (Sir.24.21). No one can have enough of such feasts or ever suffers from squeamishness because he has had too much: the more he drinks from that source the greater will be each man's capacity and eagerness for more.

If you depart from evil but fail to do good, you transgress the law, which is fulfilled not simply by abominating evil deeds but also by performing good works.