Reading Perry Miller's book, Roger Williams (publ. 1953). Seems a good place to start (all over again). Miller tries to get behind the image made useful for later generations & political developments (Williams the genial forerunner of religious tolerance).
Miller's Williams is an adamant, uncompromising spiritual perfectionist, one who followed out his premises to their inexorable conclusions. Not the future-foretelling prophet, but the prophet as pain in the neck.
Also a kind of poet. "Mainstream" Protestantism, from the beginning, was totally opposed to allegorical readings of the Bible. Hence all the New World forms of covenanting & congregating, which attempted to re-enact - literally - the language, law & rituals of the Old & New Testaments. But Williams was a radical typologist - the stories in the Bible were mere figures, allegories, "types" - of that unwritten Someone - God on earth.
"Deep in Williams' being lay an aptitude for figures and allegories; nothing for him was more congenial, as nothing was more antipathetic to Winthrop, that to conceive of historic Israel as an allegory of a church which exists not on land or sea. Winthrop might be compared to - he was more generous than - a modern man of affairs, brought up on Longfellow, when confronted with T.S. Eliot or Kafka. As for Williams, being a rhetorician of allegory, he could not bear to see Charles I or Governor Winthrop take unto themselves those accoutrements of power which Christ had turned into metaphors." [p.39-40]