I believe it has to do with the nature of God, the nature of man, and the nature of sin. God, who is perfect, unlimited, eternal, infinitely holy, and infinitely righteous, can only dispense justice perfectly. God is different than us in that He is the creator, and we are the created, therefore He has a right to call to account that which He created. Our nature is limited, with limited righteousness and limited justice. Sin is an offense against God’s infinite Holiness and righteousness. Some sins are worse than others, and some sins, (mortal sins) deserve death. Since the sins we commit are against one who is infinite, the offense is infinite. The length of punishment must be unlimited, but God is even merciful to those in hell by not giving those there infinite suffering. God burns with hatred against wickedness and sin.
The nature of man is that he is limited but unlike animals who are annihilated at death, man has an immortal soul that persists forever after death, and it will persist in the state of our own choosing. Now is the time for salvation! At death the will is forever set either for God, or against God. No one would reject Him if they saw Him as He is, so we are given a limited time to make our own determination of our fate, whether to live for Him or against Him when we can’t see Him as He is. He is putting us to the test.
Part of the nature of sin is that it distorts. It distorts our perception. It distorts our sense of justice, but even we who have a limited sense of justice consider some offenses severe enough to deserve life imprisonment, or even death. If we consider some offenses severe enough to deserve death, then why doesn’t God have that same right who has a perfect sense of justice. We all know that our justice system is flawed. It’s flawed because it is limited due to our limited nature. Our sense of justice is also distorted by sin because we allow grave injustices like abortion to become law. Due to mans limited nature he is incapable not only of not being able to dispense perfect justice, but to even fully understand what perfect justice is.
If we are both incapable of dispensing perfect justice, and we create unjust laws then what right do we have of crying foul when the one who is capable of dispensing perfect justice does so? What right does the creature have to cry foul of any action of the Creator? We don’t!
Sin distorts our perception of reality. When we live in a state of mortal sin our perception of reality is completely distorted. That distortion is removed through contrition, and repentance through the Sacrament of reconciliation, and frequent reception of the Eucharist. The nearer we draw to God the clearer reality becomes.
God’s justice is tempered by His mercy in part I believe because we truly don’t understand how badly we offend Him when we sin. Jesus said on the cross, “Father forgive them for they know not what they do!” His mercy is infinite since He is an infinite being, and it requires infinite mercy to forgive sins committed by finite beings against the infinite being of God. Those sins committed by the creature against the creator. God has perfect righteousness, and justice, which always has to be in a state of balance. To let wickedness and sinfulness on our part go without perfect justice would create imbalance. There always has to be perfect equilibrium before God. Everything must be in perfect balance and harmony. But because God is an infinitely loving God, He devised a way to both maintain the equilibrium of His justice, and forgive us, so we could be brought to the perfect state which He intends for us. The way God chose to balance His perfect scale of justice was by He Himself receiving the justice which we ourselves deserve and could not satisfy. It also gave Him the opportunity to love as deeply as love could go… all the way, by suffering torture and death for us so we wouldn’t have to.
So instead of looking at the reality that justice must be served before God. Either through Jesus sacrifice of the cross, or by us paying it ourselves through eternal separation from God, justice will be served and the scale of justice will be balanced.
It is only when we want to be our own gods and choose wickedness over holiness and righteousness, and choose to live contrary to the laws of God that we cry foul at the prospect of His perfect justice.
Not even the rich man who asked for Lazarus to dip his finger in water to cool his tongue said he had received an unjust sentence. What he did say was “Can I go warn my five brothers so they will not also come to this place of torment?”
Seek the Lord while He may be found, call to Him while He is still near. So rather than worrying about whether an eternity in hell is just or not, why don’t we do whatever we can to avoid it?