He doubled the number required; partly to oblige Saul the more to the performance of his promise; and partly to show his great respect and affection to Saul's daughter.
Related Commentaries of 1 Samuel 18:27
1 Samuel 18:27
27 Wherefore David arose and went, he and his men, and slew of the Philistines two hundred men; and David brought their foreskins, and they gave them in full tale to the king, that he might be the king's son in law. And Saul gave him Michal his daughter to wife.