In 1622, Berthold Niehus moved to Cologne, where he visited the house of proselytes, founded the Brotherhood of the Holy Cross.
After his conversion to Catholicism Niehus sent letters to professors Georg Calixtus and Konrad Hornejus in which he explained his reasons for joining the Catholic Church.
The main motive of the treatment was the need for the Chief Justice, which could explain the Bible and put an end to theological debate and controversy, and so the judge in his opinion is the Bishop of Rome.
Berthold was running in Hildesheim, where he became a canon of the Church of the Holy Cross, where later moved to Holland, where he met with Gerhard Vossius.
A few years later he moved to Mainz, where he entered the service of the Bishop Johann Philipp von Schönborn, on whose behalf in 1654 went to Ingolstadt to collect information about the institute of diocesan priests, headed by Bartholomew Holzhauser.