Just as the power of evil works by persuasion, not by compulsion, so does divine grace. In this way our liberty and free will are preserved. If a man commits sins when he is subject to the devil, he himself pays the penalty, not the devil, since he was impelled to evil not by force but by his own will. It is the same where a good action is concerned: grace does not ascribe this action to itself but to the man, giving him the credit for it, since he is the cause of the goodness that befalls him.
Grace does not make a man incapable of sin by forcibly and compulsorily laying hold of his will but, though present, allows him freedom of choice, so as to make it clear whether the man’s own will inclines to virtue or to evil. For the law looks not to man’s nature but to his free power of choice, which is capable of turning towards either good or evil.
~St Makarios of Egypt
Prayerful Life 