In short only an eternal punishment is fitting for sins committed against an eternal God.
An eternal punishment is only unfair to those who fail to understand the nature of God, the nature of man, and the nature of sin. While God is loving, kind, and merciful, He is first and foremost a holy and righteous God. So holy is He that he cannot tolerate sin. As far as man is concerned he is corrupted by sin, and that sin is always directly against God. And as to sin’s nature God hates it so much that sin has forever separated us from himself since God cannot tolerate even the slightest degree of sin. As a result, all sin requires an eternal punishment. God’s holy, perfect, and infinite character has been offended by our sin. Although to our finite minds our sin is limited in time, to God—who lives outside of time—the sin He hates goes on and on. Our sin is eternally before Him and must be eternally punished in order to satisfy His holy justice.
To look at it another way since we live in God’s universe we violate His commands when we commit moral crimes. God’s the person offended. We can understand human justice. If we murder someone we realize that we can face a lifetime of quarantine for our crime since we view human life so highly. The punishment lasts for the entire duration of our human existence. Similarly, if we commit a crime (or sin) against a spiritual or eternal being a person is placed in a quarantine for the duration of their spiritual existence. Since their soul lasts an eternity, their “prison” sentence is for the duration of their soul. They’re placed in an eternal quarantine. Since God is infinitely more valuable than any person the nature of the punishment is going to be infinitely greater. And by nature, offending an infinite being incurs an infinite debt. And this is why eternal punishment is just.
Hell is the place where those whose sins haven’t been forgiven will serve their eternal punishment. But fortunately, as we will discuss in tomorrow’s devotion, there is an alternative place where even the vilest of sinners can spend eternity in, if they only make peace with their God. And that place of course is heaven and making peace with God comes only through accepting Jesus Christ as our sin substitute.