Why did Massachusetts expel Roger Williams?

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.