The protagonist of Asimov's Caves of Steel, Elijah Baley, uses 'Jehoshaphat!' as an exclamation instead of 'Jesus!' throughout the book.
Why does he do this? From the book, it seems that the Bible is still relevant in the context in which the book takes place. The protagonist cites some passages from the Bible in the book, and at some point, he clearly says the Bible is still considered sacred to almost half of the population of the Earth.
However, it is not explicitly mentioned that Christianity, as we know it today, still exists. So it could be that people are believing in a new Judeo-Christian faith based on the Bible. Indeed, Jehoshaphat is real figure from the Bible, so maybe he is the main character of such a faith. However, this is purely my opinion, and the book seems silent on the matter.
All in all, why does the protagonist use the exclamation 'Jehoshaphat!' instead of 'Jesus!'?