The above was - for me at any rate - a truism of science.
An hypothesis which explains everything is un-dis-proveable. It could be so inclusive as to explain whatever happens - to include all opposite happenings; or (and this seems common) an hypothesis is so vague and imprecise, or so highly abstract and remote from experience and observation, as to be essentially disarticulated from any possible counter-evidence.
How about religion, theology, and Christianity in particular - does the above maxim also apply?
Yes it does apply. Any religious theory or belief which explains everything is immune from counter example, which means that it is detached from observable reality - past, present or future.
I think it is inevitable that metaphysical beliefs are of this kind - that they are assumptions which structure our interpretation of experience and observation, but can neither be confirmed nor refuted.
What of the nature of God? Is knowledge of the nature of God a metaphysical assumption which explains everything and is immune to all possible eventualities; or is understanding the nature of God a matter of experience (including revelation) and observation (things that happen to us and which we perceive), which can therefore be modified by experience and observation?
For classical theology, the nature of God is (par excellence) described in terms of an hypothesis which explains everything - God is described as containing everything, the creative source of everything, sustaining of everything - all powerful, present everywhere, all-knowing...
Therefore this is an hypothesis which is immune to all possible experience and observation (including being immune to all actual and conceivable sources of revelation - such as scripture or personal revelation).
Therefore the classical theological explanation of God is on the one hand irrefutable, and can be believed with absolute security - but at the cost of explaining nothing (and, by the way, rendering revelation superfluous).
The 'pluralist' understanding of the nature of God is a consequence of experience and observation - especially of actual revelations as derived from specific writings and persons (potentially including ourselves).
The pluralist God does not explain everything - and therefore the understanding of a pluralist God could be shaped and even refuted by events.
To believe in a pluralist understanding of God is to acknowledge a radical insecurity in terms that contradiction, exposure of error is always theoretically possible - not that it is a realistic possibility for a person of solid faith.
A Man may have total confidence in his knowledge of God and his relationship with God - but this confidence is not a confidence which comes from knowing a priori that whatever happens could not in principle refute him.
The confidence of a Man of solid faith in a pluralist God is that some things will not happen. Total confidence that future events will not, as a matter of fact, be such as to refute his understanding.
Not because future events cannot refute faith, but because they will not refute faith.