John Winthrop significantly influenced the development of the Massachusetts Bay Colony primarily through his role as its first governor. His leadership helped to establish the colony's social and political framework, and he promoted the idea of creating a "city upon a hill," which articulated a vision of the colony as a model Christian society.
While Winthrop did advocate for moral and religious values, he did not encourage people to find God without the help of ministers, nor did he convince leaders to separate church and state. Instead, he supported a theocratic government where Puritan religious leaders held considerable power. Regarding the issue of enslavement, while there were varying views among settlers, Winthrop himself did not advocate for a ban on slavery.
In summary, the most accurate response regarding Winthrop's influence is that he was chosen to be governor of the colony.