C.S. Lewis’s The Great Divorce is the tale of individuals attempting to get to—or running away from—heaven in the afterlife. Their inability to get to heaven on their own is usually due to some lingering sin, an evil attached to them that needs to be relieved from their person in order to receive true absolution. Lewis’s narrator witnesses this process several times, but more often than not, people choose to hold on to their qualms or return to the Grey Place from whence they came. Many of these qualms boil down to short-sightedness or idolatry, but Lewis argues that they all have the same effect: separation from Heaven, which is separation from God.
Though Lewis is not throwing Christian theology in your face, he is clearly working as the Christian apologist here. His depictions of Hell and (almost?) Heaven are fantastical and of his own imagination, but their nature, if not their appearance, agrees with the Christian Scriptures: Heaven is the presence of God, only to be received when one admits their sin, their inability to solve it, and their need for God. Hell is the absence of God, the presence of one’s sin, and the dreadful eternity of grey living with no purpose.
Lewis’s message is clear: there is no mingling of good and evil. One must give up all evil in order to cross over the mountains and join God in his Heaven. They cannot make it up the rocks with their sensitive half-bodies, half-spirits on their own. They cannot take their malady or their sin with them. They must be free and clear of all of it in order to live eternally in the light. With even a speck of evil in them, or a refusal to admit a need for God, they remain in the in-between place, or take the bus back to the Grey Place to remain for eternity or try again later.