The men tell the priest to be quiet probably to avoid Micah’s attention. That Micah has not been mentioned in the preceding verses suggests that what has been happening at his house has been without his awareness. The priest’s first responsibility in this encounter was to notify Micah of the presence of the Danites. So this command to keep quiet is basically a command for the priest to betray his master.1
19 And they said to him, “Keep quiet; put your hand on your mouth and come with us and be to us a father and a priest. Is it better for you to be priest to the house of one man, or to be priest to a tribe and clan in Israel?”