The main purpose of this legislation is to change the rules around who can become a U.S. citizen. Specifically, it aims to prevent anyone who has entered the United States unlawfully from being eligible for naturalization, which is the process of becoming a U.S. citizen. The key provision of this legislation is a clear statement that anyone who has entered the country illegally will not be able to apply for citizenship. This rule overrides any other immigration laws that might have allowed for exceptions or different eligibility criteria.