Convened by Pope Innocent III, the Fourth Council of the Lateran gathered in Rome with representatives from across Christendom, resulting in one of the most significant assemblies in medieval Church history. Among the 400 attendees were bishops, abbots, and theologians who aimed to confront various issues facing the Church, including heresy and the need for spiritual reform. Due to the rise of dualist movements, such as Catharism, the council sought to define and clarify Catholic doctrine in a manner that would unify and strengthen its teachings.

At the heart of the assembly was the definition of transubstantiation, articulated by theology luminary Thomas Aquinas and adopted by the majority of the Church leadership. This doctrine posited that during the Mass, the bread and wine used in the Eucharist would not merely represent but truly become the body and blood of Christ. This notion of transubstantiation was crucial, as it not only underscored the mystery and sanctity of the sacrament but also differentiated Catholic practice from Protestant interpretations that would arise later. The language around this doctrine presented a clear contrast to various radical movements of the period, reinforcing the authoritative interpretation of the sacraments as understood by the Catholic Church.

In addition to matters of doctrine, the Fourth Council of the Lateran also dealt with issues such as clerical reform and the relationship between the Church and secular authorities. Notably, the council established canons that enforced capital penalties for certain heretical beliefs and mandated the establishment of a regular annual synod to ensure ongoing governance and discipline within the Church. These laws and doctrines had lasting consequences, shaping Catholic liturgical practices and ecclesiastical authority for centuries to follow, particularly in light of the Reformation and the ensuing debates on the nature of the Eucharist.