Despite differences in cultural religions and death, what we believe is more fundamental to who we are as human beings than what we know.
This is a thesis statement for The Management of Grief by Bharati Mukherjee and David Sedaris' Jesus Shaves.
How would I use this as a conclusion to my essay paper?
The first confusion here is that a thesis statement normally appears at the beginning of a paper rather than in the conclusion. At the end of the paper, you can state how whatever evidence you have provided actually does support your thesis, but you should not just have a verbatim restatement of your thesis.
As a statement, it is somewhat unclear. The first element you need to define is what you mean by the phrase "despite differences in cultural religions and death." "Cultural religions" is not normally a term used in English. Do you mean "despite different cultural and religious attitudes about death?" In both stories, the authors explore the intersection of different cultural and religious traditions, but Mukherjee is far more focused on death and grieving than Sedaris.
The notion that our belief systems are more important in determining who we are than our actual accumulation of factual knowledge seems a major theme in Sedaris' story, but if you intend this as a thesis, you will need to work to explain how it is relevant to Mukherjee.
In order to use this statement either as part of the introduction or conclusion of your paper, you will need to specify what it means in the context of both stories and finish by summarizing how your evidence leads to a conclusion.