"Now Nadab and Abihu, the sons of Aaron, each took his censer and put fire in it and laid incense on it and offered unauthorized fire before the LORD, which he had not commanded them. And fire came out from before the LORD and consumed them, and they died before the LORD." (ESV)
God's worship was serious business in the Old Testament; and its even more so, in the New (Testament). Nadab and Abihu thought they were doing God good service--even going above and beyond the call of duty. God killed them.
What is the New Covenant church to offer God today? We cannot offer sacrifices for sin--since Jesus only did that, one time; and His is the only atonement accepted by God (cf. Heb. 9:24-26). But we may offer sacrifices of praise, as per Heb. 13:15. Especially in church worship, let us do only what God commands, (or else be willing to suffer the consequences).
[Puritan quote of the day: "For any to say that, though their mind be ignorant yet their heart is good, they may as well say that, though they are blind yet their eyes are good." --Thomas Watson, in "The Beatitudes"]
