Final answer:
Roger Williams founded Rhode Island to end state interference in church affairs and ensure religious freedom and tolerance.
Step-by-step explanation:
Roger Williams was motivated to establish Rhode Island as a colony primarily because he sought to end state interference in church affairs.
Williams believed in complete freedom of religion, which set him apart from the Puritan oligarchy of Massachusetts.
His views on the separation of church and state and his condemnation of the Puritans' taking of Native land led him to purchase land that would become Rhode Island, where he would offer refuge to those suffering religious persecution and practice religious and social toleration.