[quote=@Ayazi]
This has got me thinking of an idea that Saint J was originally supposed to be summoned as a servant for a member of the Assembly but instead became Bailey Clarkes servant.
[/quote]

The summoning's just done off of the basis of the catalyst used, if any, and the compatibility between the Master and Servant as assessed by the Grail.

The Church is neutral in this war, and the representative from the Church and the Servant Ruler are cooperating as overseers of the war. We do have one Master from the Church, but that's because she's being renegade rather than because she's a Church rep.