The concepts of Piotr Skarga, contained in the Sejm Sermons, make him appear to us not so much as a priest and theologian, but as an outstanding lawyer with extensive knowledge in his field. This Jesuit preacher, however, was not a jurist by training, although in his work he establishes the definition of law and introduces distinctions between its variations. Skarga believed that the creation of normative acts should be commissioned only by persons who have specific knowledge and expertise. Moreover, in his opinion, the proper functioning of the state is not be possible without the application of a fair laws, equal to all. It is worth noting that unjust laws are mentioned by the Jesuit preacher in the Sejm Sermons as one of the six diseases of the Polish-Lithuanian Commonwealth.