1 Samuel 17

"So Saul clothed David with his armor, and he put a bronze helmet on his head; he also clothed him with a coat of mail. 39 David fastened his sword to his armor and tried to walk, for he had not tested them. And David said to Saul, “I cannot walk with these, for I have not tested them.” So David took them off." v.38-39

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David comes to the battle after shepherding that same day, robed in his light attire.  That he was able to wear Saul's armor shows that he was probably a full grown man by this time.  David tries on this armor for battle and not having every dressed like so he tells Saul that he cannot wear it in battle.  His quickness and agility would be more hindering than helpful facing the heavy weight giant Goliath.  How often do our leaders put on too heavy a burden on us that we are not ready to carry or don't recognize our ability in who we are knowing our own strengths?  But David was not afraid to tell Saul that he couldn't wear the armor and his reason why (not just out of pride that he knew himself better).  We do see that after David has killed Goliath that he pulls out his sword and cuts off Goliath's head showing that he did have more than just his slingshot and stones yet that was all he need to kill him.  What armor has been placed on you that you are not ready to fight with?