Maybe I am wrong, but I thought the point of the OP was to discuss whether "there is no health in us" (as meant by the authors of the BCP) rather than prove the existence of God. Perhaps Rhiannon would comment.
I don't see how the latter can be separated from the former given that the text in question in the OP is a Christian text (the word 'health' in this particular context is a specifically Christian one which is not going to be recognised by the average GP, for example), and Christians are I'm told given to believing in God for some reason.
So which questions about Christianity would not need us to first prove the existence of God?
A bit like if you or anyone else might like to discuss the inns and outs of the Harry Potter books as though they are stories of real events that actually happened.
If it was the Harry Potter books that were asserted as actual events, you might expect to see some white coated figures hovering about in the background; had you proved the Harry Potter books, to be stories about actual events that had really happened the white coated figures wouldn't have any other choice than to quietly back away.
I think that illustrates how a lot of atheists might see what it is you're saying Ailen.
ippy
Please answer my question. Which questions about Christianity would not need us to first prove the existence of God?
There are certainly some, such as establishing whether there was a historical Jesus at all, and ascertaining what he may reasonably supposed to have said and did if such as figure did exist (this is quite different from the point ippy appeared to be making, claiming an exact parallel between Jesus and Harry Potter - for as far as I'm aware, no one is arguing that Harry Potter ever existed).
Now a lot of Christians may insist that the historical existence of Jesus can in no way be separated from his supposed divinity, or his having performed miracles, or there being a spiritual dimension to life at all. I don't see why that has to be.
Conversely, atheists like ippy seem to accept the same view of the matter as some Christians - namely that the historical Jesus cannot be separated from supernatural claims he made or are made about him - which of course they do not believe in. I find such an approach inherently boring and repetitive, just as I find the former fantastical and totally unbelievable.
There is also the question of whether some of Jesus moral teaching has any true relevance for the present day, and that also can quite easily be separated from supernatural claims.
In other words - a plague on both your houses!