Note:
Sanctification, the ongoing process of becoming holy, is assuredly not an instantaneous once-and-done event. It is a lifelong process, a quest, a journey, a seeking, a falling down and getting up again. It is, of course, driven by God. God cultivates the desire for holiness, sows the seeds in us, gives the growth, prunes the unhelpful and irregular, season after season after season.

Quote:
“We may, indeed, be sure that perfect chastity — like perfect charity — will not be attained by any merely human efforts. You must ask for God’s help. Even when you have done so, it may seem to you for a long time that no help, or less help than you need, is being given. Never mind. After each failure, ask forgiveness, pick yourself up, and try again. Very often what God first helps us towards is not the virtue itself but just this power of always trying again. … It cures our illusions about ourselves and teaches us to depend on God. We learn, on the one hand, that we cannot trust ourselves even in our best moments, and, on the other, that we need not despair even in our worst, for our failures are forgiven.” (p. 93-94)

Source: Lewis, C.S. Mere Christianity. New York: Macmillan, 1960.