It forces the gestapo to go door to door (i.e., expend human resources). Many jews disappeared from western countries simply because the nazis used the civil records first -- it detailed what everyone's religion was where they lived. Who needs to go door-to-door when you can use centralized records to pinpoint exactly where you need to be?

Hide the messages telling your neighbor they're on the way/the ones you received saying the same so you could get yourself in order as needed.