Why did the Council of Tours order sermons to be delivered in rustic Roman language in 813?

The Council of Tours issued its decree in 813 because of the intellectual reforms initiated by Charlemagne.1

During his reign, Charlemagne sought to restore Latin to its "pure" Classical standards, as he was concerned that contemporary usage had significantly declined. This effort, led by scholars such as Alcuin of York, highlighted the growing divide between the refined Latin used by the clergy and the evolving vernacular spoken by the common people.12

As it became increasingly evident that the vernacular and Latin were no longer the same language, the Council of Tours decreed that sermons should be delivered in rusticam Romanam linguam ("in the rustic Roman language"). This measure was intended to ensure that the message of the church remained intelligible to the congregation, as the "purer" Latin promoted by the Carolingian renaissance had become inaccessible to the average listener.1