John Wesley on 1 Samuel 17:51

David took - Hence it appears, that David was not a little man, as many fancy; but a man of considerable bulk and strength, because he was able to manage a giant's sword. The stone threw him down to the earth, and bereaved him of sense and motion; but there remained some life in him, which the sword took away, and so compleated the work. God is greatly glorified, when his proud enemies are cut off with their own sword.