Oh, the irony. The Philistines were the enemy only a boy named David had defeated. Now God used them to save David from Saul. Hmm.
Has God ever been merciful to you, a sinner? Sometimes it's trouble with a little "t" and sometimes it's trouble with a capital "T." It's a good thing to say like David, "Behold, God is my helper, the Lord is the sustainer of my soul...for He has delivered me from all trouble."