 John Sigismund gave the Reichshof Castrop to his teacher and educator Carl Friedrich von Bordelius, whereas he received the territories of Cleves, Mark, and Ravensberg in the Treaty of Xanten in 1614.John Sigismund's most significant action was his conversion from Lutheranism to Calvinism, after he had earlier equalized the rights of Catholics and Protestants in the Duchy of Prussia under pressure from the King of Poland.He was probably won over to Calvinism during a visit to Heidelberg in 1606, but it was not until 1613 that he publicly took communion according to the Calvinist rite.