In essence, the Massachusetts Bay Colony expelled Roger Williams for having the wrong beliefs. His expulsion also happened because he was a threat to those who held political power. This happened in 1635.
Roger Williams got in trouble for two main reasons. First, he did not think the Puritan church in New England was pure enough. He thought it should break more definitively away from the Church of England. Second, he argued that the government should not be able to tell people what sort of religious behaviors they should engage in. This was a real problem in a society in which the government and the church were so closely connected.
Because of ideas like this, Williams was expelled from the Massachusetts Bay Colony.
Roger Williams was expelled from the Massachusetts Bay Colony because yes of his beliefs, but also because of his preaching. He was preaching of the separation of church and state, which back in that time, was unheard of- Anne Hutchinson was also expelled from the Massachusetts Bay Colony because she preached of salvation through God's grace rather than salvation through good works. Her as well as Roger Williams helped to pave the way for the "Great Awakening" which was a religious revival and would occur a bit later. Roger Williams as well as Anne Hutchinson ( and two others), after being kicked out of their colonies, gained land rights and formed the Rhode Island Colony-which was free when it came to religion!