About that number six, he says:
In the exercise of divine worship, certain solemn, public rites should be preserved that aim at good order and decorum and were introduced by the pious consensus of the whole church. Therefore the protection of ecclesiastical rites, which were approved by serious consideration and which give useful instruction concerning many topics in public assemblies, also pertains to the ecclesiastical ministry. Nor should a minister change them, leading to scandal in the church, because of some private desire of his mind. Consequently, the sixth duty of ministers is the preservation of ecclesiastical rites.—Johann Gerhard, On the Ministry II, p. 101.