The main purpose of this legislation is to establish St. Patrick's Day as an official Federal holiday in the United States. This aims to recognize and celebrate the cultural significance of St. Patrick's Day, which is observed on March 17th each year. The key provision of the legislation involves an amendment to an existing law that lists Federal holidays. Specifically, it adds St. Patrick's Day to this list, indicating that it will be recognized alongside other Federal holidays. This means that on this day, Federal employees would typically have the day off, similar to other holidays.