This article examines the manuscript, entitled Jesus Nazarenus Legislator, written by Adam Boreel against the De Tribus Impostoribus. The analysis focuses on three main aspects of the manuscript. First, I give some information about De Tribus Impostoribus. Second, I trace the history of the writing of Boreel’s book. To this end, I will mainly take into consideration the correspondences of Henry Oldenburg and John Worthington. Last, I show that Boreel postulates a rational Christian religion and that he places emphasis on the practical aspects of this religion. For this reason, all humankind can accept it. In conclusion, I will sum up the results obtained from my analysis of the Jesus Nazarenus Legislator; I will also suggest that Boreel’s ideas could be read in light of the discussion on adiaphora in the Christian religion.