Um, Saul brought the evil on himself. In choosing to defy and deny God (who is good) he quite naturally brought on good’s ‘opposition’ which is evil. God ‘permits’ evil as a natural consequence of the Fall and as a free will choice of men. From it (evil) He will somehow, in some way, be able to have good come from that evil.
Here is a limited example.
A man is shipwrecked on an island. Bad, no?
He has to work very hard to provide himself with food, clothing and shelter. Along the way he suffers more than if he were living comfortably and ‘easily’ in a place where he could easily find, raise or buy the food, clothing and shelter.
Even if this man is shipwrecked and lives the rest of his life alone and in want. . .can ‘good’ come from this?
Yes, it can. In being away from the distractions of wealth, the man can, in humility, realize how ‘little’ he is compared to God. He can be thankful even for the little he has, realizing how easily he could have nothing. In such ways this man who, had he lived an ‘easy life’ might have drifted away from God, might in the ‘hard life’ become truly holy and close to God.
Now we don’t see ‘the big picture’. But God does. Just because we can’t ‘imagine’ good coming from a given ‘evil’ act doesn’t mean that it doesn’t happen.