What exactly is a drive-in service?
It means people listen to the message from parked cars as opposed to inside the chapel.
A lot of churches have a small radio transmitter for less than $100 that has about a half block radius. It’s tied to their sound system and members can drive to the parking lot and listen to the pastors message on their car radio. Many are just doing Facebook streaming for their services but a few members are not internet savvy and don’t want to be thus the parking lot broadcast.
Over 50 years ago I can remember going to mass at a drive in movie theater. You took the big old speaker and hung it on your car window. They set up a stage up front where they placed the altar right in front of the movie screen.
You have the service with people in the parking lot in their cars.