'The Selling of Joseph,' a sermon by white clergyman Samuel Sewall, first published in Boston in 1700, became the first public anti-slavery treatise. Liberty, he wrote, being 'The real value unto life; none ought to part with it themselves or deprive others of it but upon mature consideration.' A strong anti-slavery treatise for its time, Sewall's writing provoked slaves in Boston to mount a determined effort to obtain their freedom.