Why do Clemens's encounters with the Campbellites matter? Simply put, because the Campbellites were not as benign as they are usually represented. The sect was virulently anti-Catholic, theological allies of the Know Nothings of the 1840s and '50s. The religious bias was deeply ingrained in Campbellite doctrine, which in its most extreme form identified the pope with the Antichrist or the Beast prophesied in Revelations 20. Clemens never entirely outgrew his anti-Catholic prejudices, and his lifelong antipathy for Catholicism may have originated, ironically, in the Campbellite sermons he heard as a child. For good or ill, the Campbellites left a mark on young Sam Clemens.