The 15th ed. of the Chicago Manual of Style opts for the latter.

The possessive of a title or name is formed by adding ‘s. This is so even when the word ends in a sibilant, unless the word itslef is formed from a plural. (5.25)

The general rule covers most proper nouns, including names ending in s, x, or z . . . (7.18)

They do make exceptions for names of two or more syllables that end in an eez sound (7.20), names ending with an unpronounced s like Descartes (7.21), and “For . . . sake” expressions like “For Jesus’ sake” (7.22; but note the follow up example of “Jesus’s contemporaries”).

They are not hard-nosed about the general rule:

But if a word ends in a sibilant, it is acceptable (especially in journalism) to use a final apostrophe without the additional s. (5.25)

Those uncomfortable with the rules, exceptions, and options outlined above may prefer the system, formerly more common, of simply omitting the possessive s on all words ending in s. (7.23)

Pronunciation seems to be the guiding principle:

This practice . . . reflects the way possessive forms are generally pronounced . . . (7.17)

Though easy to apply, that usage [of "omitting the possessive s on all words ending in s] disregards pronunciation and seems unnatural to many. (7.23)

I see no mention of an exception for biblical names, which is an exception I’ve heard from various authors.

I realize CMOS is not the end-all for these sorts of questions, though it is our guide at Wipf & Stock. Indeed, The Dictionary for Modern American Usage states the following exception: “Biblical and Classical names ending in -s take only an apostrophe” (509). It notes in parenthesis “No extra syllable is added in sounding the possessive form.” I’m not sure I agree. When spoken the possessive of Jesus comes out “Jesusses.” Or, at least it does when I talk. But, I’m from Texas.  We’re not known for proper pronunciation. At any rate, I am inclined toward the pronunciation logic of CMOS. It seems to me that the addition of an apostrophe and another s would account for this pronunciation.

Any thoughts?

[I'd like to take up split infinitives in a future post.]