Almost all of us—even if we don’t do it consciously—look early in an essay for a one- or two-sentence condensation of the argument or analysis that is to follow.
This sentence or two that captures your position on the main idea of the paper and tells the reader what your essay is going to be about is what we call a Thesis Statement. It can be defined as:
A thesis statement appears near the beginning of the introductory paragraph of a paper, and it offers a concise solution to the issue being addressed. It states the claim of the argument presented in a paper, and sometimes a brief summary of all explained reasons in the paper.
You should provide a thesis statement early in your essay — in the introduction, or in longer essays in the second paragraph — in order to establish your position and give your reader a sense of direction.
The thesis statement should be flexible enough to include any new information discovered later on or something that you have missed out earlier. Therefore, it is better not to finalize it till the end of the paper so as to leave a room for modification at any junction of your thesis/dissertation writing.