Christian thematics and mythology include the conception of “purifying” yourself so that you can get into Heaven. Purifying yourself essentially involves figuring out how to deal with eternal happiness and instant gratification, among many other of God’s amazing and wondrous gifts, and not letting these gifts either go to your head and cause you to run wild with ego, or to make you get bored with them and toss them away.
The way this is typically held to happen is, after death, the spiritually impure goes to an intermediate place between the material world and Heaven called Purgatory. There they, well, purify.
What is purification? It’s when you stop giving time and energy and attention to things that aren’t good for you and give that time instead to higher pursuits. An example of this is going to rehab. Hopefully you don’t just rid your body of drug-induced sickness, but you also reflect on why you became an addict in the first place.
This answer illustrates how difficult it is to purify oneself. The author got the drug out of his body, multiple times, but had no idea how to actually exist as a non-addict. So he took the path of least resistance right after leaving rehab.
The way out of this is to admit you don’t have control over the problem. This is the first step of a 12 step program. You allow other people, and God, to help you. Purifying means to give up the lower aspects of self, ego, self-loathing, destructiveness, in order to embrace endless positivity and grace.
Once you’ve tasted God’s gifts, and your only response to them is “more!”, that’s when you know you’re ready for heaven. You’ve open fully to God, given Him access to your whole being, willing to let Him chart a path for you through Heaven.
But yeah, if you spurn God’s gifts, don’t believe they exist, aren’t even interested in finding them while on Earth, then you won’t even think to go look for them in the afterlife. It will be dark, cold, away from even the fires of Hell. And even if you think to yourself, well, the Christians believed in Heaven, let’s try to find that. And you’ll go to Heaven and the warmth and light won’t feel welcoming. They’ll suffuse into your soul and start stripping it away of your flaws and weaknesses. It’ll feel like you’re getting burned up. God doesn’t want you to totally get obliterated, so He won’t let you get too close.
If you want to stay, you’ll have to choose to purify yourself. An angel will lead you down to purgatory, and you’ll start learning what you have to do to be able to stay in Heaven. The cleansing won’t be pleasant, but when you’re done, you’ll feel like a new person. Then when you go towards Heaven, it won’t feel like you’re burning away your individuality, because you already gave those lower aspects up.