The heart
"But the LORD said to Samuel, "Do not consider his appearance or his height, for I have rejected him. The LORD does not look at the things man looks at. Man looks at the outward appearance, but the LORD looks at the heart."-1 Samuel 16:7
Many people use this Scripture saying that God looks at their heart (positives), unlike man who is always judging them and their outward appearances(negatives). What is obvious in the context of this Scripture is not that Samuel is looking at the negatives in Eliab and God is looking at the positives in him; but just the opposite! Samuel thinks that Eliab looks fit to be a king. that he has good qualities. To Samuel, he is qualified. I can imagine God saying it like this, "Samuel, you're seeing everything all fine and dandy on the outside, but you're not seeing what I'm seeing. I'm looking at his heart." It reminds me of exactly what Jesus was saying on one occasion,'Watch out for false prophets. They come to you in sheep's clothing, but inwardly they are ferocious wolves."-Matthew 7:15