The article points out that the Greek organizations are permitted to be explicit about their leadership. I would assume they’re permitted to insist that the leader be a member of the group. A 3D leader has to be a 3D.
Just my guess. Don’t know if I’m right or not.
The Christian group, though, covers a lot of Christian denominations. That’s probably why they went general with: “must have a personal commitment”. My guess is they were trying to parallel the “must be a Lamda” thing that the Greeks get away with.
I think I’d say they use: “must be a member (or equivalent term used by) of some Christian church”.
Thank you for sharing your insights, dear brother in Christ!