Matthew 25:46: "And these shall go away into everlasting punishment:but the righteous into life eternal." (KJV)
Revelation 22:11: "He that is unjust, let him be unjust still:and he which is filthy, let him be filthy still:and he that is righteous, let him be righteous still: and he that is holy, let him be holy still." (KJV)
ANSWER: (a) Punishment relates only to the guilt of sin. Forgiveness removes the liability to punishment. It does not remove regret for sin in time nor in eternity. In this sense sin casts a shadow into heaven itself. In other words you cannot forgive the sin which God has forgiven. Nor does God, who forgives a sinner in middle life, restore the blessings lost in his wasted youth, such as education, and intellectual power and possibly physical health lost by sins against his body. The prodigal son was received by his Father, but the money lost by riotous living was not restored in the form of a second division of the paternal estate. Then again others suffer in consequence of one man's sin whose forgiveness does not arrest these evil consequences, such as the poverty of the drunkard's wife and children. His reformation and conversion to Christ does not restore the farm which has gone down his throat and lodged in the till of the saloon. I speak with deliberation and reverence when I say that God cannot forgive the natural consequences of sin, because he cannot change the past. To do so would falsify history. He is a God of truth. He can no more change the past than he can change the multiplication table. (b) There is a sense in which sin is its own punishment, as virtue is its own reward. Yet as this reward differs from that which God will bestow in heaven, so this punishment must differ from that which he will inflict in hell. What this final reward is, and final punishment, has not yet been revealed. It awaits the Day of Judgement. Hence in preaching it may not be best to make this distinction between natural consequences and penalty. There is a poem relating to an impenitent sinner, the last verse of every stanza ending thus:
"To be left alone with memory
Is hell enough for me."
Yet I cannot believe that such expressions as "the wrath of God," "the Day of Judgment," and "eternal judgment" are rhetorical figures for the natural consequences of sin. In that case the final sentence of the Judge would be superfluous. The assertion that the moral law automatically inflicts penalty on transgressors is a doctrine which strongly leans toward the denial of the existence of a personal moral Governor. I lay no foundation for pantheism.
— from Steele's Answers pp. 49-51.