Christianity Before Christ.
John G Jackson.
Very scholarly work showing how all the features of Christianity were present in all the old myths way back before ever Christian times.
The very origin being in fact a anthropomorphised version of the journey of the sun through the heavens.
The very kind of story telling that we find in Australian aboriginal myths.
Fascinating read. Available for free at the intenet archive: https://archive.org/details/christianitybefo00