It is a "recognised exception" that while something that belongs to Jones is "Jones's" and an object that Chris owns is Chris's, when it comes to
Biblical names it is "Jesus' cross", "Moses' staff". Although that makes me shudder when I try and type it in without 'mistakenly' putting "Jesus's cross" or "Moses's staff".
I'm pretty much presuming that this particular irregularity comes from the earliest English writings[1]. For similar reasons, look at the irregular verbs in all languages that have them (those that are not artificial, and have had not had
massive reforms put forward by some historic ruler or government) and it's the common words. "To be." I am, you are, he is, I was, they were, etc. c.f. (not respectively)
From my appallingly rusty French... Je suis, il est, ils sont, nous sommes
From my never-that-great German... Ich bin, Du bist, Es ist, Wir sind;
Some probably misremembered Italian fragments... io sono, voi site, noi siamo
Spanish snippets, probably wrong... Yo soy, Nosotros somos, ustedes son, usted es
I tried
looking up Japanese, but what little knowledge I already possess does not extend to understanding what I found.
[1] Which will have been largely ecclesiastical in nature or otherwise biblically inspired, being written with the loose (or disputed) sense of rules that was the attitude of the time, but meant that once the grammatical standards started to be set in concrete there was an obvious need to take account for this whole swathe of non-standardisation. In the "Biblical names" case, then probably driven by a "You can't change the Word Of God!" attitude. Albeit that this had been (mis-)translated several different times before it was eventually set down in English calligraphy or even early print. However, that's just my impression.