If we think of Jesus as merely a man, then this question is a natural one to ask. But the reason Jesus did not have to spend eternity in hell is that He is not merely a man, but the God-man. The second Person of the Godhead took on flesh and lived among men in the form of a man. But He was a man like no other because His nature was that of God—holy, perfect and infinite.
Several passages attest to this fact, such as the opening passage in John’s Gospel. It is there we read the following:
“In the beginning was the Word, and the Word was with God, and the Word was God. He was with God in the beginning. Through him all things were made; without him nothing was made that has been made. The Word became flesh and made his dwelling among us. We have seen his glory, the glory of the One and Only, who came from the Father, full of grace and truth” (John 1:1–3, 14).
This passage gives clear testimony that the eternal Word, who is co-eternal with God and of the same essence as God, took on human flesh and made His dwelling (“pitched his tent” or “tabernacled”) among us. As the apostle Paul says regarding Jesus, “For in Christ all the fullness of the Deity lives in bodily form” (Colossians 2:9).
With that in mind, let’s look more closely at the question. It is certainly true that the penalty for our sins is an eternity in hell. The Bible says that all have sinned (Romans 3:23) and that the wages of our sin is death (Romans 6:23). The book of Revelation says that those whose names aren’t in the Lamb’s book of life are cast into the lake of fire where they will be tormented “forever and ever” (Revelation 20:10, 15).
But how can the death of Jesus atone for the sins of every person who has ever lived? This is where the discussion of Jesus being the God-man comes in. If Jesus were a mere man (with sin of His own), then His death wouldn’t even atone for His own sin, much less the sins of another. But Jesus is no mere man; He is God in human flesh. As a man, He can identify with those for whom He sacrificed Himself. As a perfectly sinless man, He can atone for the sins of mankind without first having to atone for His own sin. Finally, as God, He can fully satisfy the wrath of God that our sins incur.
Sin against an infinite God must be paid infinitely. That is why payment for our sin must be infinite. There are only two options for infinite payment. Either a finite creature (man) must pay for his sin for an infinite amount of time, or an infinite Being (Jesus) must pay for it once for all men for all time. There are no other options. A sin against an infinitely holy God requires an equally infinite satisfaction as payment, and even an eternity in hell will not dissipate God’s infinite, righteous wrath against sin. Only a divine Being could withstand the infinite wrath of a holy God against our sin. It requires an equally infinite Being as a substitute for mankind to satisfy God’s wrath. Jesus, as the God-man, is the only possible Savior.