'Olam HaBa', the Next World, exists beyond time. Once this universe ends, after infinity, Olam HaBa will be. This isn't a simple truth and it's a totally different discussion.

Every person is born Pure. Throughout their lives they are made impure by performing misdeeds and can purify themselves through repentance. Cycles may repeat themselves due to misdeeds by ancestors or previous lives but a person is not made impure by these cycles unless they repeat them.

If a person dies with impurities they may choose to reincarnate. If so, they are born with a clean slate but will have many challenges to overcome based on their misdeeds in previous lives.

This whole cycle began after the fall of Adam. This Original Sin has not yet been rectified for the whole world and each of us as individuals will eventually be faced with a facet of that challenge. On top of that, every generation since Adam with few exceptions has added to the pool of misdeeds, thus causing greater and greater quantities of hurdles for succeeding generations to face. Again, even though the amount of challenges has been increased every person is still born pure and can potentially finish their lives with a clean and clear slate.