Beginning in chapter 24, three stories are presented that give us some insight to one particular aspect of David’s morality.
On the run from Saul, David takes refuge with his rag tag group of disaffected citizens in a cave. Saul comes along with his 3000 elite troops but, needing a “pit stop” goes to relieve himself in the very same cave.
David’s men urge David to make an end of his pursuer, but David will not raise his hand against God’s anointed. He refuses to return evil for evil.
Saul returns evil for David’s good. Nabal (chapter 25) returns evil for David’s good. Saul returns evil again for David’s good in chapter 26. But David not only doesn’t return evil for good, he doesn’t even return evil for evil. As the proverb goes, quoted by David, “from evil doers come evil deeds.” David refuses to allow himself to be coerced into evil simply because others do him dirty and not only that, he rebukes his men for even suggesting such a thing.
This is an ethic echoed by Jesus when he said “Love your enemies and pray for those who persecute you” and even more directly by Paul in Romans 12:17 “Do not repay evil for evil.”
I must say, however, that there is a difference between refusing to repay evil for evil, and refusing to deal with evil. That will become a problem for David later.