God is first identified as a “consuming fire” in Deuteronomy 4:24 and 9:3. The writer to the Hebrews reiterates, warning the Hebrews to worship God with reverence and awe “for our God is a consuming fire.” There is nothing mysterious about the Hebrew and Greek words translated “consuming fire.” They mean exactly that—a fire that utterly consumes or destroys. How, then, can a loving and merciful God also be a consuming fire that utterly destroys?
In both Deuteronomy passages in which God is called a consuming fire, Moses is speaking first to warn the Israelites against idolatry (Deuteronomy 4:23–25) because God is a “jealous God” and will not share His glory with worthless idols. Such behavior provokes Him to a righteous anger which is justified when His holiness is disrespected. In Deuteronomy 9:3, Moses again refers to God as a consuming (or devouring) fire who would go ahead of the Israelites into the Promised Land, destroying and subduing their enemies before them. Here again we see God’s wrath against those who oppose Him depicted as fire that utterly consumes and destroys anything in His path.
There are several incidents in which God’s wrath, judgment, holiness or power are displayed by fire from heaven. Aaron’s sons Abihu and Nahab were destroyed by fire when they offered a profane sacrifice, “strange fire,” in the tabernacle, a sign of their disregard for the utter holiness of God and the need to honor Him in solemn and holy fear. The confrontation between Elijah and the prophets of Baal on Mount Carmel is another example of consuming fire from God. The prophets of Baal called upon their god all day long to rain fire from heaven to no avail. Then Elijah built an altar of stones, dug a ditch around it, put the sacrifice on the top of wood and called for water to be poured over his sacrifice three times. Elijah called upon God and God sent fire down from heaven, completely consuming the sacrifice, the wood, and the stones and licked up the water in the ditch. Then His anger turned against the false prophets and they were all killed. When prophesying the destruction of the Assyrians, who resisted the true and living God and warred against His people, Isaiah refers to the tongue of the Lord as a consuming fire and His “arm coming down with raging anger and consuming fire” (Isaiah 30:27–30).
God’s holiness is the reason for His being a consuming fire, and it burns up anything unholy. The holiness of God is that part of His nature that most separates Him from sinful man. The godless, Isaiah writes, tremble before Him: “Who of us can dwell with the consuming fire? Who of us can dwell with everlasting burning?” Isaiah answers this by saying that only the righteous can withstand the consuming fire of God’s wrath against sin, because sin is an offense to God’s holiness. But Isaiah also assures us that no amount of our own righteousness is sufficient (Isaiah 64:6).
Fortunately, God has provided the righteousness we need by sending Jesus Christ to die on the cross for the sins of all who would ever believe in Him. In that one act, Christ mitigates God’s wrath, exchanging His perfect righteousness for our sin. “God made him who had no sin to be sin for us, so that in him we might become the righteousness of God” (2 Corinthians 5:21). All the wrath of God was poured out on Jesus, so that those who belong to Him would not have to suffer the same fate as the Assyrians. “It is a fearful thing to fall into the hands of the living God” (Hebrews 10:31), but we need not fear the consuming fire of God’s wrath if we are covered by the purifying blood of Christ.
 Got Questions Ministries. (2010). Got Questions? Bible Questions Answered. Bellingham, WA: Logos Bible Software.