In his sermons on capital sins, Alain argued that sodomy and homicide are the most serious sins, since they call forth the wrath of God, which led to the destruction of Sodom and Gomorrah. His chief work on penance, the "Liber poenitenitalis" dedicated to Henry de Sully, exercised great influence on the many manuals of penance produced as a result of the Fourth Lateran Council. Alain's identification of the sins against nature included bestiality, masturbation, oral and anal intercourse, incest, adultery and rape. In addition to his battle against moral decay, Alan wrote a work against Islam, Judaism and Christian heretics dedicated to William VIII of Montpellier.