Without it a man would have no fitness to enjoy the life to come. Heaven is a holy place. The Lord of heaven is a holy Being. The angels are holy creatures. Holiness is written on everything in heaven.
Death works no change.
The grave makes no alteration. Each will rise again with the same character in which he breathed his last. Suppose for a moment that you were allowed to enter heaven without holiness. Their pleasures are not your pleasures, their tastes not your tastes, their character not your character. There will be none such in heaven.