I don't know about the laws of Pennsylvania, but here in Georgia any church, or any other kind of private facility, can have armed staff members or volunteer guards from the congregation. That's been legal in Georgia for several years, if the management of the church grants permission to GWL (carry permit) holders to have firearms at the church. It doesn't have to be permission that's specific to any individual. Permission to any one regular private citizen has the effect of making it legal (not a criminal offense) for any other GWL holder to carry there, also.
Now if the place of worship is also a SCHOOL, and many churches do have private Christian schools as part of the same campus, then the school weapons law must be followed. For private schools who aren't controlled by the County Board of Education, that school's management can give written permission to carry. The permission has to be in writing, has to be for a limited time period (I'd say one year is good), and has to identify the particular individual and the specific gun(s) that person is authorized to carry.
More churches and private schools should take advantage of these provisions in Georgia law, and have some armed staff members or armed volunteer guards to be ready to shoot-down some lunatic or jihadist who barges into the place with mass-murder on his mind.