I think that, when you die, you just have to judge yourself, to face what you have done, . Are you ready to take all the love that's offered to you ? Do you believe you deserve it ? Would you dare to leave behind you everything you long for in your earthly life ? If you do, then you may stay if you wish to. Otherwise, you forget about your previous existence, and are sent back down there, with a chance to live a good life this time.
That's the difference between heaven and hell. If you love yourself, you need nothing more to be happy, you're in heaven (loving yourself doesn't mean being egoist, it means being contented with what you do, being able to watch yourself in a mirror and telling yourself you're proud of what you've become, you need nothing more now). If you hate yourself, then you may see what hell is. For a while, before forgetting and being reincarnated.

I have lived before. Some lives are crystal clear. others are somewhat spotty.

I can offer no proof of this claim. It's not important whether I am believed or not. These are personal experiences which are as real and as useful as anything else in my past.

There is nothing really mystical or spooky about the whole thing. It's totally natural. The ancients used the analogy of "changing one's clothes" to describe this phenomena. The world wide symbol in nature used to describe it was the snake, or serpent. The snake by shedding it's skin thereby renewing itself, demonstrated the dropping of a body and gaining another.

The word "reincarnation" is not the best way of describing what goes on after body death. Reincarnation implies, someone or something determining where you are to go next. For the most part, you determine your existance beyond body death. WE use the word "reincarnation" for lack of a better word

To answer the OP's question of what was the spirit or doing during the 40 years in between lives. Agian, it's pretty much up to the individual. There are no set rules to follow and it varies from each individual. Some tend to hang around longer than usual when the body has not been properly disposed of. Others hang around if an injustice was done to them. Old grave yards are a good place to find the latter.