Schoolhouse Rock! is a series of short, animated videos that use music to teach about grammar, science, economics, history, mathematics, and civics. The aim is to help kids learn things like historical facts and multiplications tables by learning songs.
In American schools, it's common for kids to have to learn the Preamble to the United States Constitution by heart. This song, from Schoolhouse Rock, is meant to give these kids a hand, even though it is a slightly abridged version.