What are "exceptional circumstances" when applying from another university?

Hi!
I'm a student in year 13, who was rejected from Oxford this cycle (for law). I have offers from from a couple of other good universities, but my heart is somewhat set on Oxford. Furthermore, I've bee considering doing a different course, as whilst I enjoy the idea of Law, I think I would rather study Philosophy and Theology, and then convert into a law career later.

Unfortunately, for reasons I don't really want to go into, taking a gap year and re-applying like that is not a possibility for me. Furthermore, I do not mind incurring extra total student loans by starting a course at another university, applying to Oxford whilst there, and then potentially leaving the course early if I am offered a place.
Oxford says on their website that they allow applications from students currently in other universities. However they have a bit of confusing phrasing. They say "We will only consider such applications in exceptional circumstances and you should make very clear in your application why you do not wish to continue on your current course. Please note we are not able to give examples of these exceptional circumstances as applications will be considered on a case-by-case basis."

Obviously I understand why they can't explain, but it makes my life a bit harder, since I don't know if "I want to explore my passion for Philosophy/Theology and regret applying for law straight up" is a good enough answer for them. Does anyone here have any advice or experience with this, and may be able to guide me a little here? I don't want to waste money, and a lot of time, applying for a second time if they're doing to reject me straight up because of this. Thank you so much for any help.