Even if you could enter heaven without holiness, what would you do?
What joy would you feel there?
What holy man or woman of God would you sit down with for fellowship? Their pleasures are not your pleasures. Their character is not your character. What they love, you do not love.
If you dislike a holy God now, why would you want to be with him forever?
If worship does not capture your attention at present, what makes you think it will thrill you in some heavenly future?
If ungodliness is your delight here on earth, what will please you in heaven, where all is clean and pure?
You would not be happy there if you are not holy here.