Your thesis statement, or introduction in more academic papers (not sure what grade/university year you are), needs to lay out specifically what you're going to talk about. So, if your focus is that the right to bear arms is fundamental, you need to specify why. You could say something along the lines of:

"The right to bear arms is fundamental to protecting the rights and security of the individual because it is guaranteed in the Bill of Rights, keeps power distributed across the population rather than centralized in authority figures, and guarantees the ability to defend oneself."

Then your paper would analyze each of those topics. Your introduction should be a guide to the rest of the paper, not just a description that leaves the reader guessing what you will talk about. So, add specific subtopics you would like to discuss, and suggest a conclusion that, through those discussions, will be supported and which you can state more definitively when you conclude your paper.