In the theological polemics against the Prague masters, he was the main spokesman for the Taborites and their most important theologist.

His treatise Confessio Taboritarum (Confession and Defense of Tábor) was significant in the international Reformation literature and is known from 16th and early 17th century prints.

He first spoke as a representative of the Taborites at a meeting of the Hussite theologians of Tábor and Prague in the house of Petr Zmrzlík in December 1420.

In 1444, the provincial congress approved the theological positions of Jan Rokycana and the teaching of the theologians of Tábor was condemned as false.

In August 1452, however, Tábor also surrendered to George and Mikuláš was imprisoned in the Old Town Hall until he promised obedience to Jan Rokycana.

According to his doctrine, in the elements of the Eucharist (the bread and the wine) the body of Christ is present only spiritually and sacramentally.

To the faithful who receive the sacrament properly, Christ gives "life, pasture, delight, spiritual help, consolation, and satiation."

The Bible alone should be the foundation of Christianity; the doctrines of the Church are from fallible men, and can only be accepted if they are in accordance with the law of Jesus Christ.