It was so radical because it was one of the first major documents regarding rights of people and limiting the power of monarchs. For example, it prohibited things like cruel and unusual punishment or it established that right to free speech in the parliament was a must and that parliament members can't be prosecuted for their work in the government. The ideas of it were mostly taken from John Locke who was a popular philosopher at that time. The bill of rights inspired many other documents like the United States constitution and their bill of rights.
