There is a reason why we are offended, indeed angered by the story of Uzzah and the story of Nadab and Abihu. We find these things difficult to stomach because we do not understand four vitally important biblical concepts: holiness, justice, sin and grace. We do not understand what it means to be holy. We do not understand what justice is. We do not understand what sin is. We do not understand what grace is.
– R.C. Sproul, The Holiness of God, Tyndale House Publishers, Carol Stream, Ill., Copyright 1985, Kindle Edition