Jacob was born in 1372 in Stříbro (called Mies in German and Misa in Latin) near Plzeň in Bohemia (present-day Czech Republic).
He studied at the University of Prague, receiving both bachelor's and the master's degrees in theology, and became pastor of the Church of St. Michael and an outspoken supporter of Jan Hus.
[1]: 51 His study of Scripture and the Fathers led him to believe that withholding of the chalice in the administration of Holy Communion to the laity was an arbitrary measure of the Catholic Church.
[4]: 51 In 1414, he propounded and defended his views in a public disputation; and when Hus, at that time attending the Council of Constance in Konstanz before his arrest, accepted them to some degree, Jacob began to administer the chalice to his parishioners, in spite of the remonstrances of the bishop and the university.
[5]: 180 Though Jacob would by no means submit, he was not removed from his office, perhaps because in other points, as, for instance, in the doctrine of purgatory, he agreed with the Catholic Church.