In most sifre Tora (Torah scrolls), 240 columns of text each start with the letter vav (ו), and five do not. The first of those five exceptional columns, of course, is the first column of the Torah, which starts with a bes (ב); the other four start with the letters י (B'reshis 49:8), ה (Sh'mos 14:28), ש (disputed location; see e.g. Minchas Shay to Vayikra 18:8), and מ (also disputed; see e.g. Minchas Shay to Bamidbar 24:5).
At each of the exceptions, there's a masoretic note (duplicated in most print chumashim) that indicates the anomalous column with the phrase "בי״ה שמ״ו סימן", "'בי״ה שמ״ו' is a mnemonic device". Indeed, that's a nice mnemonic, and the phrase comes from T'hilim 68:5.
But it's clearly not meant as only a mnemonic device because — and here's the kicker — a specific column is designated as the vav of that acronym. That same note appears on the word "וְאָעִידָה" (D'varim 31:28), which is at the head of a column.
So what's the deal? Specifically:
- Why is this acronym important, beyond serving as a mnemonic device? (After all, the designation of a specific column as the vav indicates that there's more to it than merely serving as a mnemonic.)
- Why are those six words at the heads of the anomalous columns; or, why are those six columns the anomalous ones? Especially, why is "וְאָעִידָה" listed as the sixth of the lot?