A couple of facts to remember about this. The church that this bill is meant for at least initially who wanted to do it is a huge church. It has about 4000 members, it has a seminary, a school and daycare. Second the officers would be sworn officers so they could only enforce state law it can be likened to many colleges have a police force for their property, they can only patrol on their property and enforce state laws. Fourth, the ACLU of Alabama has already said they will sue over this.
But churches have kind of done this to a degree already. The Mormon University BYU and the Catholic Notre Dame both have their own police force love.