1 Samuel 16:7

But the LORD said unto Samuel, Look not on his countenance, or on the height of his stature; because I have refused him: for the LORD seeth not as man seeth; for man looketh on the outward appearance, but the LORD looketh on the heart.

 What we don't understand sometimes is that everything that looks good is not necessarily good. Samuel went to Jesse's house to anoint the next king from his brood of sons. God had chosen one of the sons, but He did not give Samuel the boy's name before Samuel arrived. Samuel polled all of Jesse's sons, and mistakenly thought, at first, that the oldest son would be the one. And why not? Traditionally, the eldest son in Israelite families received the blessing, not to mention that Jesse's oldest son was tall, dark and handsome! God quickly corrected Samuel and told him that it was not about his looks. 

God knows the heart of every human being. God knew the heart of the man we know as the man after HIs own heart, the sweet psalmist of Israel, and the mightiest king of Israel's history. He knew that David would be imperfect but repentant. God knew that David would love the LORD with all his heart, and he would fight tooth and nail for the people of Israel. 

Next time we are tempted to look at someone and think that they are so great or so terrible because of how they look, remember Samuel. We see the exterior, but God judges the heart.