Justin and Hailey Bieber want their formal wedding celebration to be a religious affair because they feel bringing God into their marriage will make their union stronger ... this according to Stephen Baldwin.
Stephen was on his way to the New York State Fair -- where he's launching a new initiative for veterans called Ready Vets Go -- when he filled us in on the motives behind his daughter and the Biebs' formal wedding party.
Justin's father-in-law says the happy couple understands weddings and marriages are supposed to be a holy commitment, and they feel a religious ceremony will go a long way towards finding peace and happiness together.
Justin and Hailey enjoyed a fancy lunch together Thursday at E Baldi ... so ya can't argue with Stephen, they're definitely having fun!
As we first reported ... Justin and Hailey are going to say their "I dos" again in a place they've fallen for ... South Carolina ... and they recently sent out their save the dates. Hailey's dad tells us they're still deciding between a couple venues.
Justin sang in front of his church earlier this week in Bev Hills ... and Stephen says Justin and Hailey's church friends will be at the ceremony, along with tons of celebs.