Returning home, David and his men find the Amalekites raided and kidnapped their families. This is a new low, and they talk of stoning him (as Israel did of Moses just before the Exodus). But He seeks God who promises victory if they go after the raiders. God grants them victory, and David makes sure the background men are rewarded along with the front line fighters. He also sends some spoil to Judah.
Saul doesn't fare as well.
The Philistines win the battle, Saul and his three sons all die, and the Philistines take his body, armor and some cities.
How this is about Jesus
To be saved, the old man, the first Adam, our sinful man has to die. Saul represents this.
David represents the second Adam, Christ raised and exalted to the throne.
Israel not only talked of stoning Jesus, they did it.
David saves physical life of his and his men's families; Jesus rescues souls.
When you are in a fix and discouraged, strengthen yourself in God (30:6).
After a victory it's easy to be hard on others. Show mercy (30:22-25).
Unfaithfulness will bring you to a bitter and shameful end (31).