 He became "ḥakam" in Middelburg and, after 1643, in Amsterdam, where he was engaged also as teacher in the Talmud Torah.He vocalized the entire "Mishnah" which was printed in 1646 at the establishment of Manasseh ben Israel, with the anonymous collaboration of Adam Boreel.Jacob caused a great stir by a plan, drawn by him, of Solomon's Temple.