In the last decades of the 18th century, a few Polish dioceses were governed by representatives of the Catholic Enlightenment. Their pastoral activities focused on the reform of the priesthood and, especially, on the duty of preaching. Despite being perceived as members of a single group, their ideas differed to the point of being mutually contradictory. Interpretation of the ideological differences among these bishops is the preliminary aim of the paper. I examined pastoral letters and preacher handbooks written by four of these bishops: Michał Poniatowski, Ignacy Massalski, Wojciech Skarszewski, and Porfiriusz Skarbek-Ważyński. However, my main concern is the social practice of parochial preachers in their dioceses. I was interested in the methodology of sermonizing, the frequency of preaching topics, and the style and content of homilies delivered by clergy. I based my research on pastoral visitations, especially from the Diocese of Płock, providing information about the printed collections of sermons used by parochial clergy as well as the texts they wrote. The main conclusions are as follows: the clergy adopted to some extent only those reforms which were adjusted to their parochial needs and were supported by administrative pressure. Regardless of theoretical programs, preaching in the Commonwealth was changing in the direction of “Enlightened Tridentine Catholicism.” This means that the clergy accepted an enlightened style and language and a focus on morality, but not models of social and natural worlds. However, by rejecting the latter, they avoided enhancing the process of division between popular and elite.