Sometimes theists challenge atheists about what evidence would be required before they would believe. Various unlikely scenarios are offered in reply. I have taken the bait myself in the past.
I think the correct answer is much more ordinary. If the god of christian theism did exist a lot of simple things would just make more sense.
The evidence would not show beyond all doubt that the diversity of life rested on millions of years of relentless competition, death and destruction. Life would not have been all but wiped out in mass extinctions at least five times in its history.
The predominant economy in the natural world would not be parasitic and predatory. The world really would show the loving qualities of its maker without having to ignore the majority of the facts.
The bible really would contain prophecies that could be verified using objective historical evidence. It wouldn't be necessary to rip verses out of context and interpret ambiguous phrases to try to make details fit post hoc..
The bible would contain useful information that people could not have known at the time it was written.
The ethics of scripture would be enlightening and uplifting without exception. It would condemn things like slavery unambiguously and champion the rights and equality of women. It would not advocate moral evils that need to be explained away with appeals to relativism and special pleading.
Miracles would really happen - even now in the age of CCTV, smart phones and scientific enquiry. It would require stubbornness rather than healthy skepticism to deny them.
Natural disasters would not kill millions of earth's inhabitants. The planet would not be designed to destroy life.
Prayers would get answered reliably. Confirmation bias would not be necessary. The prayers of believers would have real and observable power.
There is so much more detail I could add to this, but in summary it would be more difficult to reject the claims of christianity than to accept them. It is not too much to expect that this should be so.