A thesis statement is vital to have in your introduction.
Without a thesis statement, it is like traveling to an unfamiliar place with no GPS/navigation tools. Tell us the journey we are about to embark upon.
Usually these statements are 1-2 sentences long, and usually are at the end of the introductory paragraph.
The statement should be strong and clearly expresses a major argument. Not too broad.
Thesis statement should not be belief statements.
The statement should appear in your introduction, but also is part of the summation in the conclusion.
Leave out the obvious and unnecessary..."in this paper I will" instead get right to the argument.
Before research, construct an idea of your thesis, but let the sources you locate further shape your statement.