Leviticus 10 records the consequences of improper worship. That is, worship according to human design and not according to the revelation of the Lord. Ross remarks, Where Scripture clearly prescribes what should be done or directly prohibits what should not be done, there is no room for innovation and alteration.
1 It is likely that Nadab and Abihu had no malice or wickedness in their hearts when they did this. They may have even prepared for this service with sincerity and reverence. Nevertheless, the Lord is swift to pour out his judgment upon them. While proper attitudes are important in worship, so too is proper obedience. Calvin wrote, If we reflect how holy a thing God's worship is, the enormity of the punishment will by no means offend us. Besides, it was necessary that their religion should be sanctioned at its very commencement; for if God had suffered the sons of Aaron to transgress with impunity, they would have afterwards carelessly neglected the whole law. This, therefore, was the reason for such great severity, that the priests should anxiously watch against all profanation.
2 The worship of God should never be characterized by carelessness, especially by those who have a spiritual leadership role.
2 And fire came out from before the LORD and consumed them, and they died before the LORD.