A fair part of the book of Exodus is comprised of instructions for the building of the tabernacle and its furniture and the resulting construction. Moses was commanded, "And see to it that you make them according to the pattern which was shown you on the mountain" (Exodus 25:40; see also 25:9; 26:30). From the tent curtains to the furniture inside, specific instructions were given as to how everything was to be made. When the tabernacle was set up by Moses, a cloud covered it and the glory of the Lord filled it (Exodus 40:33-35). It was an exciting time for the people of Israel.
Detailed instructions were given for the elaborate process to consecrate Aaron and his sons as priests (Exodus 29). Aaron and his sons were washed with water and they were dressed in the special garments made for them. They were anointed with oil and sacrifices were offered. Blood was put on the tip of their right ears, the thumb of their right hands and the big toe of their right feet. For seven days Aaron and his sons stayed at the door of the tabernacle (Leviticus 8).
On the eighth day, offerings were made on the altar in the tabernacle courtyard and at the completion of the offerings, the glory of the Lord appeared to the people and fire came from before the Lord and consumed what was on the altar, making a huge impression upon the people (Leviticus 9:23-24).
Up to this point, everything was done according to the instructions of the Lord. Unfortunately, two of Aaron’s sons, Nadab and Abihu, decided, for whatever reason, to put fire in their censers and incense in that fire as an offering to the Lord. Fire came from before the Lord again, but this time it killed these two men (Leviticus 10:1-2).
What a harsh punishment! Nadab and Abihu were not guilty of idolatry or sorcery. They were not guilty of sexual immorality, violence or even murder. Nevertheless, they died swiftly at the hand of the Lord. What could be so terrible about offering fire and incense to the Lord?? Isn’t that what priests are supposed to do, make offerings?
We are informed by the author Moses that these two men were offering "profane fire" (NKJV), an offering which the Lord had not commanded them (Leviticus 10:1). Clearly, the Lord did not accept their offering, regardless of how sincere, enthusiastic or well-meaning they may have been. The Lord told Aaron through Moses that those who "come near" Him must regard Him as holy. The Lord must be glorified before the people by those who "come near" (10:3).
It is no small thing to ignore the Lord’s instructions about worship, about anything! God is not glorified when I worship Him according to my own desires. Nadab and Abihu learned too late that God doesn’t accept just any worship that is offered to Him. Our worship must be according to the "pattern" which He has revealed in His word.