The world is governed by the system of the Tree of Knowledge Good and Evil. When people connect to the good side of the Tree with their actions they bring balance into their lives and souls.
Before a soul comes down to the world she is put on a scale that measures to see if it is heavier on the right or on the left.
The soul is inserted into a proper body to continue its correction process. When the left is strong the soul becomes ‘oppressed’ in a negative vessel and the Tikkun is harder.
These souls have the challenges but at the same time greater rewards when they are able to remove the negativity from their vessel.
The system works on individual and generation levels. A generation may have a similar type of souls that requires similar or shared Tikkun. The consciousness of parents from a specific generation affects their children and future generations.
Rabbi Yochanan tells us that
“אין בן דוד בא, אלא בדור שכולו זכאי, או כולו חייב”.
“the son of David (Mashiach) comes only in a generation that all the people have merits or in a generation that all are wicked ”