I think it's simple.
If your beliefs aren't relevant to the position you're being employed to fill - for example, if you're a married gay maths teacher at a Catholic school - then you should be able to hold that position. One the other hand, if you want to be a priest and yet also want to be married to your gay partner, then you aren't fit for the job.
If Thorburn can't advocate for gay inclusion, etc., at EFC because his religious affiliation won't allow it, then he's not fit for the position.
If your beliefs aren't relevant to the position you're being employed to fill - for example, if you're a married gay maths teacher at a Catholic school - then you should be able to hold that position. One the other hand, if you want to be a priest and yet also want to be married to your gay partner, then you aren't fit for the job.
If Thorburn can't advocate for gay inclusion, etc., at EFC because his religious affiliation won't allow it, then he's not fit for the position.