Why was David not punished for acting like a priest when Uzzah was struck dead?

The key is to keep the two men straight, because they are easily confused. The one struck dead for touching the Ark was Uzzah, in Second Samuel chapter six. He was not a priest, and when the oxen stumbled and the Ark began to tip he reached out and took hold of it. On the surface that looks like he was helping, but the law was clear that no one but the priests was to touch the holy things, and God struck him on the spot, so that even David became afraid. Uzzah was not acting like a priest; he was handling what only the priests were permitted to handle. The man who was actually punished for acting like a priest is a different person: King Uzziah, in Second Chronicles chapter twenty-six. When he grew strong he became proud and went into the temple to burn incense on the altar, which belonged to the priests alone, and God struck him with leprosy that he carried to the day he died. That is the real case of a king reaching into the priestly office and being judged for it. So why was David not punished? Because David did not usurp the priesthood the way Uzziah did. When he ate the consecrated bread it was out of genuine need while doing the Lord's work, and Jesus Himself later defended it against the Pharisees, teaching that the Sabbath was made for man, not man for the Sabbath. The sacred things are good when they are used rightly, for man's true benefit. And when David moved the Ark and Uzzah died, David took the lesson to heart: the second time, he had the Levites carry it the way God had commanded, with fear and reverence. God sees the heart, and He knows the difference between a man acting in humble need and a man grasping at an office out of pride.