Why Hell is necessary for the eternal punishment?
Belief bears the seed of a sort of Paradise experienced by the spirit, while unbelief contains the seed of a sort of Hell, which is again experienced spiritually. Just as unbelief is the seed of Hell, so too, Hell is a fruit of unbelief. As unbelief is the cause of entering Hell, it is also the cause of Hell’s existence and creation.
For if there is an insignificant ruler of small dignity, small pride, and small majesty, and an unmannerly one tells him rebelliously, ‘You cannot punish me!’ for sure, if there is no prison in that place, the ruler will have one built for him and will cast him in it. However, by denying Hell the unbeliever contradicts the infinitely Powerful One, Who has infinite dignity, glory and majesty, and is infinitely great, and is accusing Him of impotence and lying, he is severely insulting His honor and dignity, and offending His pride, glory and majesty in awesome and rebellious manner. Certainly, if to suppose the inconceivable, there was no reason for the existence of Hell, it will be created to punish unbelief, which comprises contradiction of God and insulting Him with impotence to such degree, and such an unbeliever will be cast into it.