Smith's Bible Dictionary

Fire is represented as the symbol of Jehovah’s presence and the instrument of his power, in the way either of approval or of destruction. (Exodus 3:2; Exodus 14:19) etc. There could not be a better symbol for Jehovah than this of fire, it being immaterial, mysterious, but visible, warming, cheering, comforting, but also terrible and consuming. Parallel with this application of fire and with its symbolical meaning are to be noted the similar use for sacrificial purposes and the respect paid to it, or to the heavenly bodies as symbols of deity, which prevailed among so many nations of antiquity, and of which the traces are not even now extinct; e.g. the Sabean and Magian systems of worship. (Isaiah 27:9) Fire for sacred purposes obtained elsewhere than from the altar was called "strange fire," and for the use of such Nadab and Abihu were punished with death by fire from God. (Leviticus 10:1; Leviticus 10:2; Numbers 3:4; Numbers 26:61)