If he's developing into a Calvinist...

"'If he's developing into a Calvinist or a Lutheran or an Erasmian or an Anabaptist it isn't very healthy: look at George Wishart and the Castillians.'"Sybilla is referring to the different strains of Protestant Christianity that had arisen in this era, and to the conflicts among these sects, and between Protestants and Catholics. George Wishart was burned at the stake for his Protestant beliefs.