Numbers 3:1-4 These are the generations of Aaron and Moses at the time when the LORD spoke with Moses on Mount Sinai. These are the names of the sons of Aaron: Nadab the firstborn, and Abihu, Eleazar, and Ithamar. These are the names of the sons of Aaron, the anointed priests, whom he ordained to serve as priests. But Nadab and Abihu died before the LORD when they offered unauthorized fire before the LORD in the wilderness of Sinai, and they had no children. So Eleazar and Ithamar served as priests in the lifetime of Aaron their father.
Lev 10:1-7 – 1 Then Nadab and Abihu, the sons of Aaron, each took his censer and put fire in it, put incense on it, and offered profane fire before the LORD, which He had not commanded them. 2 So fire went out from the LORD and devoured them, and they died before the LORD. 3 And Moses said to Aaron, “This is what the LORD spoke, saying: ‘By those who come near Me I must be regarded as holy; And before all the people I must be glorified.’ ” So Aaron held his peace. 4 Then Moses called Mishael and Elzaphan, the sons of Uzziel the uncle of Aaron, and said to them, “Come near, carry your brethren from before the sanctuary out of the camp.” 5 So they went near and carried them by their tunics out of the camp, as Moses had said. 6 And Moses said to Aaron, and to Eleazar and Ithamar, his sons, “Do not uncover your heads nor tear your clothes, lest you die, and wrath come upon all the people. But let your brethren, the whole house of Israel, bewail the burning which the LORD has kindled. 7 “You shall not go out from the door of the tabernacle of meeting, lest you die, for the anointing oil of the LORD [is] upon you.” And they did according to the word of Moses.
What was their sin in thus offering it? Plainly, the narrative points to the essence of the crime in calling it ‘fire which He had not commanded.’ So this was their crime, that they were tampering with the appointed order which but a week before they had been consecrated to conserve and administer; that they were thus thrusting in self-will and personal caprice, as of equal authority with the divine commandment; that they were arrogating the right to cut and carve God’s appointments, as the whim or excitement of the moment dictated; and that they were doing their best to obliterate the distinction on the preservation of which religion, morality, and the national existence depended; namely, the distinction between holy and common, clean and unclean. To plough that distinction deep into the national consciousness was no small part of the purpose of the law; and here were two of its appointed witnesses disregarding it, and flying in its face. They have had many successors, not only in Israel, while a ritual demanding punctilious conformity lasted, but in Christendom since. Alas! our censers are often flaming with ‘strange fire.’ How much so-called Christian worship glows with self-will or with partisan zeal! When we seek to worship God for what we can get, when we rush into His presence with hot, eager desires which we have not subordinated to His will, we are burning ‘strange fire which He has not commanded.’ The only fire which should kindle the incense in our censers, and send it up to heaven in fragrant wreaths, is fire caught from the altar of sacrifice. God must kindle the flame in our hearts if we are to render these else cold hearts to Him. (MacLaren)
This may be an emblem of dissembled love, when a man performs religious duties, prays to God, or praises him without any cordial affection to him, or obeys commands not from love, but selfish views; or of an ignorant, false, and misguided zeal, a zeal not according to knowledge, superstitious and hypocritical; or of false and strange doctrines, such as are not of God, nor agree with the voice of Christ, and are foreign to the Scriptures; or of human ordinances, and the inventions of men, and of everything that man brings of his own, in order to obtain eternal life and salvation. (Gill)
Hearing and reading God’s Word must come into willing, obedient, and reliant hearts. If not we will have worldly desires of what is right and wrong and try to mix the Word of God with that which is not ordained by God, nor does it give Honor and Glory to Him. The Word of God has little benefit in a disobedient heart that is set on its own desires and paths in life. Without a desire to be led by God for the single purpose of honoring and glorifying Him our hearts and minds become dull and our ears deaf and our hearts like stone. It is easy to spot and identify the first steps away from God that lead to such lukewarm commitment – Neglect and Complacency. The loss of desire to honor and glorify God is always preceded by a lacking desire to honor and glorify Him in all thoughts, words, and actions, which is closely followed by neglect of His Word. We might live content with our place in life but we should never be content with our growth, maturity, and service to God.