God is love (1 John 4:8). He who denies this does not know God. He who does not love, does not know God.
Hell is the finalisation of not knowing God and never having been known by God (Matt. 7:22-23). Jesus will say to those who say “Lord, Lord” and yet were foolish hypocrites who never practised love that he “never knew” them.
Love is not just simply a feeling that you have toward someone or mere service you give to another person. These people who Jesus condemns had indeed cast out demons in his name. They had been the people who had done extant community service in the name of Christ. They had been people who converted others, evangelised others, taught the right doctrines, etc. This is the irony of the situation. But he never knew them nonetheless because they knew not him. They had been bogged down by so many of their accomplishments, so many of their improvements on the path toward deification that they had neglected a significant piece of the puzzle. That their Christianity was not of their own but was a gift from God himself.
Love is patient, love is kind. It does not envy, it does not boast, it is not proud. It does not dishonor others, it is not self-seeking, it is not easily angered, it keeps no record of wrongs. Love does not delight in evil but rejoices with the truth. It always protects, always trusts, always hopes, always perseveres. (1 Cor. 13:4-8)
These people who boast of the demons they cast out through whatever means, or of their community service, or of their self-giving to the poor, or of other miracles they made–these people have not love for love does not boast. These people have not love for love is not self-seeking. One who loves does not do these things to receive recognition but rather may even expect to get trashed for what they do. God is love and those who know him have love. They do not boast of their accomplishments for all their accomplishments are of God.
The ones in the Gospel of Matthew cast out from God experience Hell. Hell is not knowing God. It is not being known by God. Hell is the absence of truth, being tormented repeatedly by lies and repeatedly being accused. Hell is hearing what wrongs you have committed brought up against you over and over and over again. Hell is hearing the boasts, the pride, being dishonoured by the prideful. It is a state of anger. Constant anger. Immense unhappiness. This is what Hell is.
“If you love everything, you will perceive the divine mystery in things.” (Dostoyevsky, The Brothers Karamazov 291) To love is to know God but to not love is to reject God and to reject God is to reject love. Such a torment leads inevitably to Hell for there can be no truth in Hell. When there is no truth in Hell, then one experiences the pain of living in a lie so badly that “if there were fire in the material sense, they would be glad of it, for I imagine that in material agony, their still greater spiritual agony would be forgotten in a moment” (295).