and David arose and went, he and his men, and killed of the Philistines two hundred men; and David brought their foreskins, and they gave them in full number to the king, that he might be the king's son-in-law. Saul gave him Michal his daughter as wife.
This chapter illustrates the fact that the godly often suffer through no fault of their own. It shows too that God causes even the worst intentions of the ungodly to strengthen the godly (cf. Psalms 7:12-16; Romans 8:28). We see here that the selfishness of the ungodly can produce irrational behavior (e.g., paranoia, 1 Samuel 18:12, and schizophrenia, 1 Samuel 18:11; 1 Samuel 18:17), and it leads to their ruin. I am not implying that this is the only cause of these mental problems. If we allow jealousy to take root in our hearts, it will devour us like a cancer. We should desire God’s glory, as Jonathan did, rather than our own glory, as Saul did.