We find in Leviticus 10:1-3 that the two sons of Aaron, Nadab and Abihu, were killed by fire from Yahweh.
"And Nadab and Abihu, the sons of Aaron, took either of them his censer, and put fire therein, and put incense thereon, and offered strange fire before the LORD, which he commanded them not. And there went out fire from the LORD, and devoured them, and they died before the LORD. Then Moses said unto Aaron, This is it that the LORD spake, saying, I will be sanctified in them that come nigh me, and before all the people I will be glorified. And Aaron held his peace." (KJV)
These two sons, the eldest and second eldest sons of Aaron, made a fatal and tragic mistake in their worship to Yahweh.
In Exodus 24:9-11, we read how these two sons of Aaron had seen Yahweh and lived to tell about it. Then in Exodus 28 we are told that they, as sons of Aaron, were chosen, set apart, for the priesthood of Yahweh. In Leviticus chapter 9 Yahweh was present in their inaugural sacrifice as priests. It is clear from these scriptures that Yahweh approved of these two sons of Aaron. No sooner had all of these blessings come upon them than a fatal error was made and their lives were taken. So, what went wrong here that was unforgivable by Yahweh?
Nadab and Abihu took it upon themselves to worship Yahweh in a manner that He had not prescribed nor approved. We do not come to God based on our terms of worship, but on His terms of worship.
The censors that they held in their hands were holy, set apart and consecrated, to Yahweh for the service in His tabernacle. Therefore, everything that went into those censors had to be holy or set apart. The instructions for the censors had not come yet. Those instructions did not come until after they had died – Leviticus 16.
So, these two took it upon themselves to worship Yahweh in a manner He had not approved. Apparently they put fire in the censors from someplace other than the set apart altar and waved a profane fire before Yahweh. It cost them their lives.
Yahweh does not like the mixing of the holy and unholy in our worship to Him. He does not like the mixing of the clean with the unclean. We cannot choose the manner in which we worship a Holy God. We must worship Him on His terms, not our own. It is not our choice to make or call something holy that He has called unholy. Mankind can not change the mind of Yahweh about these matters.
In Samuel 6:7 we read the story about how Uzza was struck dead because he reached out to steady the Ark of the Covenant. Why was he struck dead, surely God knew the intent of his heart was pure? He was struck dead because he violated the command given by Yahweh that no one could touch the Ark of the Covenant or transport it other than the priests. They were never given approval to transport the Ark on a cart.
Many times we come to God by trying to change His laws of holy and unholy, clean and unclean. When we do this our worship is not accepted. God may not strike us dead immediately, but He does not accept our worship.
He told the children of Israel that when they worshiped Him not to do the things that the pagans do in the worship of their gods and then say that they were worshiping Him with these unholy things.
In Leviticus 10:3 it states that, 'those who come near to Him must be regarded as holy; and before all the people He must be glorified.' We must never, as Nadab and Abihu, assume to worship Him in a manner that He has not approved. When a person does this, Yahweh is not glorified by that person nor in the eyes of the people.
In Leviticus 11:43-47 we read: "Ye shall not make yourselves abominable with any creeping thing that creepeth, neither shall ye make yourselves unclean with them, that ye should be defiled thereby. For I am the LORD your God: ye shall therefore sanctify yourselves, and ye shall be holy; for I am holy: neither shall ye defile yourselves with any manner of creeping thing that creepeth upon the earth. For I am the LORD that bringeth you up out of the land of Egypt, to be your God: ye shall therefore be holy, for I am holy. This is the law of the beasts, and of the fowl, and of every living creature that moveth in the waters, and of every creature that creepeth upon the earth: To make a difference between the unclean and the clean, and between the beast that may be eaten and the beast that may not be eaten. " (KJV)
Notice in these verses that the dietary laws are connected to what makes a person considered holy before Yahweh. Just as Adam and Eve were removed from the Garden of Eden because they ate from a tree that they should not have eaten from, in these scriptures we hear Yahweh saying that we are to be holy as He is holy and then He ties this holiness to what a person eats. He declares that if we eat of the animals that He did not make for food, then we are not being “holy” as He is “holy”.
Yahweh sets the rules for those who wish to worship Him. Man cannot change those rules! Will we be a holy, set apart, people or will we choose to offer to Him that which He calls profane?
Please read the entire chapters of Leviticus 10 and 11 for further clarity.