There "may" be religious services on board but there is no guarantee. A few years ago Celebrity did have a priest or clergy program where a priest or minister would get their cabin for free but was required to perform a daily service. That program has been discontinued.
However, they do provide religious services for Catholic, Protestant and Jewish faiths during major religious holidays.
They also have a daily Catholic Mass onboard during their Holy Land Cruises
On other voyages a priest or minister, who is on board, can request time and venue for services. Or Guest Services will provide the name and location of churches in the port area.
Take care,
Mike
__________________ Cruisemates Community Leader/Moderator
"There is a great difference between being well traveled and just having been to many places." ~Me