David comes into this story as a glorious type of Christ. Goliath was a giant, but he was also a serpent, a dragon. The Hebrew word for his armor means scales, which made him a gigantic reptile, like a dragon, and David topples him with a wound to the head (Genesis 3:15). David fights him with the same weapons that he would use in fighting wild beasts. When he is done, he takes Goliath’s armor and places it in his tent (1 Samuel 17:54).
This is precisely what Jesus does when He came upon the strong man. He attacks, like David did. He is victorious, like David was. He strips the armor (panoply), as David did. He partakes of the spoil after battle (Luke 11:22). Jesus is the greatest of all giant-killers. He gives victory to His people . . . and He awakens the envy of any who would be great in Israel on their own terms.
~Douglas Wilson, blog~