To regard any suffering with satisfaction, save it be sympathetically with its curative quality, comes of evil, is inhuman because undivine, is a thing God is incapable of. His nature is always to forgive, and just because he forgives, he punishes. Because God is so altogether alien to wrong, because it is to him a heart-pain and trouble that one of his little ones should do the evil thing, there is, I believe, no extreme of suffering to which, for the sake of destroying the evil thing in them, he would not subject them. A man might flatter, or bribe, or coax a tyrant; but there is no refuge from the love of God; that love will, for very love, insist upon the uttermost farthing.
– George MacDonald, Unspoken Sermons
The key is that the treatment is medicinal. There is no medicine a parent would withhold from his child, who is dying of cancer. A extreme treatment or cure would be preferable to the loss of the life of the child. But the good news is that we ourselves can be a part of that treatment, and begin to work alongside it, and so lessen the need for the severity of the curative tonics. And when we are on board, and know that the treatment (pain, or consequences of our erroneous actions) is for the healing of our souls, then we can consent to the treatment plan, and it will be less painful. Knowledge and understanding changes so much- it makes the agonies easier to bear.