The original 1926 edition of Fowler’s Modern English Usage recommends the “prescribed usage” of shall and will, even while acknowledging that “Scottish, Irish, provincial, or extra-British” usage may not follow it.
Never mind why, but I happened to be reading the Gospel according to Luke in the “King James” translation, and I noticed an interesting use of shall and will:
9:24 For whosoever will save his life shall lose it: but whosoever will lose his life for my sake, the same shall save it.
The Greek is more literally
For whosoever desire to save his life will lose it: but whosoever lose his life for my sake, the same will save it.
Here “desire to save” is subjunctive + infinitive. This pattern is not repeated in the latter part of the verse; rather, “lose” here is just subjunctive. The verbs “will lose” and “will save” are plain futures. That’s what’s in the Greek. Nonetheless, King James’s translators make an elegant use of the resources of English in their own version of the verse. In particular, the compound “desire to save” is neatly rendered “will save”, as long as one is prepared *not* to read this as simple future.
Two verses later, we find:
9:26 For whosoever shall be ashamed of me and my words, of him shall
the Son of man be ashamed, …
In the Greek, the first instance of “shall be ashamed” is subjunctive; the second, future. According to the rule cited by the original Fowler, one might expect “will be ashamed” in the second instance: the plain third-person future. However, the Son of man his Himself speaking this sentence, so in its *meaning* the verb is first-person, and therefore “shall” is appropriate. Alternatively, the Son of man may saying what the will of the Father is; then “shall” is appropriate in this sense too, as long as the Son and the Father are not perceived as identical. Are the King James translators then making a theological statement? I don’t know.
By the way, Fowler says the OED lays out the rules for use of shall and will; but the OED missed an “ungrammatical” use of “whom” in the King James Bible:
Luke 9:18 …Whom say the people that I am?
The OED does not cite this, but it cites similar uses of “whom”, in Shakespeare for example, and calls them ungrammatical. I agree: “who” would be correct here. Now, “whom” is used in the Greek, and this may
be why the translators used it: but “whom” is used in the Greek because it is the subject of an *infinitive* verb: the literal translation would be
Whom do the people say me to be?