Someone's tried to kill you. Not once, but multiple times. He has disobeyed God. He breaks his promises.
Now you have the chance to take care of him permanently. Everyone will understand. "Justifiable self-defense," they'll say. Finally you can achieve your goals - goals to fulfill God's will and glorify Him.
Do you take that opportunity?
David didn't. The future king of Israel had been hunted down by King Saul, who had vowed to kill him. In 1 Samuel 24 & 26, David finds Saul unarmed and unaware, not once but twice. The perfect chance for David to get rid of his enemy. But he didn't.
Why not? Did our mighty warrior turn into a wimp? On the contrary, sparing King Saul's life probably took more courage and strength than any of David's feats in battle. David knew it was God's will for him to be king of Israel, but God would accomplish His will in His way and His timing. Meanwhile, for David to take action against a man God had placed as king would be wrong. "'The Lord forbid,'" David said, "'that I should...lift my hand against him; for he is the anointed of the Lord'" (1 Samuel 24:6). Then he told Saul, "'May the Lord avenge the wrongs you have done to me, but my hand will not touch you'" (1 Samuel 24:12).
We all have people in our lives who oppose us, who disobey God, or who simply can't be trusted. Sometimes they're people in authority over us. Such as political leaders.
David's example shines. He doesn't excuse Saul's actions; in fact, he reprimands him. But he leaves judgment and vengeance to the Lord. David showed Christ-like "turn the other cheek" mercy. As a result, Saul repented (for a while) and spared David's life. Grace and truth - that's a winning combination.
"Do not be overcome by evil, but overcome evil with good" (Romans 12:21).