The Zohar reveals that there are righteous souls that go into vessels/bodies and put flaws on the vessel.
This Zohar section was difficult to understand but after I read the explanation of Rabbi Ashlag I could get some understanding.
We usually think about the bodily desires and negative / flawed consciousness as ‘corrupting’ the soul. Here we read the opposite and that is difficult to understand. Rabbi Ashlag brings the example of Binah and Malchut. At the initial process of Creation, Malchut was dark and without Light of its own or even a desire for the Light. To correct that, the Creator elevated Malchut, which is the aspect of the vessel to Binah, which is the aspect of pure Light and righteous soul. Malchut experienced the Light of Binah and when it went back down to its dark place it raised the desire for the Light of Binah. The desire is the flaw because purity is a simple channel of Light without desire for the self.
Now the vessel, Malchut, needs to work harder to connect to the Light.
The righteous souls force themselves to go into a process of renewal. They may reincarnate in simple vessels to have greater ability to desire the higher levels of Light and expand their vessels.
The important lesson here is that even if we are in a happy and tranquil state of living, we need to challenge ourselves in order to expand our vessels and earn more Light. Study, share to expand your spiritual vessel, give Tzedakah and increase your tithe (gradually over the basic 10%) to expand your material vessel.