 Buckminster's close associate William Ellery Channing (1780–1842) became pastor of the Federal Street Church in Boston, 1803; in a few years he became the leader of the Unitarian movement.At first mystical rather than rationalistic in his theology, he took part with the "Catholic Christians", as they called themselves, who aimed at bringing Christianity into harmony with the progressive spirit of the time.His essays on "The System of Exclusion and Denunciation in Religion" (1815) and "Objections to Unitarian Christianity Considered" (1819) made him a defender of Unitarianism.