The most basic challenge of the spiritual life is to avoid falling into sin. It isn't easy. We all know what it is like to go to confession, having some vague hope that we won't fall into the same sins again, after having confessed; and then, soon afterwards, sure enough, we do fall into those same sins. This happens to all of us quite regularly. So it is quite obviously not an easy thing.
But another challenge, for particular kinds of temperaments especially (such as mine), is to not fall into discouragement after having fallen into those sins over and over again. We confess, we resolve; we are weak, we fail to keep our resolutions; and then we fall into those very same sins... And then we wonder: were we really even sorry in the first place? We confessed these sins, we wanted to confess them, we expressed regret, contrition, sorrow for having committed them. And then we went and committed them again - perhaps not just once again, but several times. Worse, it wasn't accidental or under pressure; it was really and truly deliberate, it was done with consent of the will. And so it hits us: how can we really say that we are sorry if we deliberately continue to do the thing for which we claim to be sorry?
This thought can torment the mind to such a degree that allows the devil to tempt us to discouragement and despair. Why oughn't we to despair? If we continually fall into the same sins, over and over, and of our own free will, how can we hope that anything will improve? We long to be free of this enslavement of the will (it is a strange thing, this confliction in the will...). But it seems so impossible, for we seem to have made no progress whatsoever. Why oughn't we to despair?
Well. There is a reason why we oughn't to despair. We have knowledge of this reason, because we have faith. But it is this faith which is being tested, in our temptation to despair. By this faith we know that God is loving, merciful, that He will forgive us if we only continue to be sorry - even if we also continue to sin. If we are the worst sinners in the world, and are yet truly sorry, genuinely wanting to be cured of our evil ways, and placing our confidence in God, He will save us. It is our will that does the trick. Even if the will is conflicted within itself, as long as we do not let the malicious will take the reins, and as long as we maintain a genuine desire to sin no more, and as long as we continue to make the effort to cooperate with God's grace - even if we fail to do so - God will save us. It is the will that counts.