If I know it too, it's not arcane knowledge, believe me! The reason that I've picked up is that Hebrew is written without vowels, so the four consonants (the tetragrammaton?) of the name used by some at least of the Old Testament people for their god were YHWH; when the merry English transliterated this, they changed the Y to a J (which they'd have been used to from Latin anyway) and the W to a V (same), and used more vowels than they strictly should have. And, with generations of hymn-singing Welsh ancestors behind me, I'm glad they did. "Guide me, o thou great Yahweh" lacks something!