 He was attacked by Johann Hornbeek ("Apologia pro ecclesia Christiana non apostatica" 1647), and by Samuel Maresius.Boreel's associates included Peter Serrarius, a fellow millenarian, Baruch Spinoza, who moved with the Collegiants after exclusion from the Amsterdam Jewish community, and Henry Oldenburg, a correspondent.Boreel was close also to John Dury.