There was already a palace chapel in the 13th century, which was dedicated to St John the Baptist. This saint and John the Evangelist are portrayed on either side of the present portal. Above them is a relief showing the baptism of Christ and the Virgin Mary holding the Child Jesus. These sculptures, as well as the pulpit and the high altar in the chapel, were created at the beginning of the 17th century by Hans Juncker (probably 1582–1624).
The church has a single nave and is divided into five bays; on each of the narrow sides there is a balcony. The altar (1609–1613) made of dark marble which goes up to the ceiling is decorated with 31 alabaster sculptures and almost 150 relief figures. Here the owner and commissioner of the palace is depicted prominently in his role as bishop, holding the model of Johannisburg Palace.
The picture programme describing the Passion of Christ, his crucifixion and resurrection, as well as the restoration and history of the altar are explained in a sound and light installation.