The main purpose of this legislation, known as the "Justice for 9/11 Act," is to establish specific legal provisions regarding the plea agreements and treatment of certain individuals detained at the U.S. Naval Station in Guantanamo Bay, Cuba, who are connected to the September 11, 2001 terrorist attacks. The act aims to ensure that these individuals can still be tried and potentially sentenced for their crimes, despite any previous plea agreements they may have entered into.