It has been asserted that on this occasion Netter converted Vytautas, Grand Duke of Lithuania, to Christianity, and was instrumental in his recognition as king and his subsequent coronation.
Although all this is doubtful, it is possible that Netter did exercise some influence during his brief stay in eastern Europe, for he has been styled the Apostle of Lithuania; he also established several convents of his order in Prussia.
The first two were presented to the pope, who on 8 August 1427, expressed his satisfaction, encouraging the author to continue his undertaking, and communicating to him the text of the Bull condemning the errors of Wyclif Dudum ab apostolorum.
It is a complete apologia of Catholic dogma and ritual against the attacks of the Wycliffites, and was largely drawn upon by the controversialists of the sixteenth and seventeenth centuries.
Among his more memorable comments, he summed up the traditional view, "In the affairs of the faith, skilled spiritual men are said to understand, the rest of the people only simply to believe".