ברוך שם

Blessed is the Name of the glory of His kingship for ever and ever. The line is said quietly all year, and aloud on Yom Kippur — and the Talmudic discussion of why is unusually candid.

A line we are not yet entitled to

The traditional account is that this is the praise of the angels, and that we say it in an undertone because it is borrowed. On Yom Kippur, when the day itself elevates the community, it is said in full voice.

Read structurally, the practice encodes a claim about the present. Shema is said aloud, because the statement that Hashem is One is available to us now — it is a matter of knowledge, and knowledge is possible in exile. Baruch shem is about malchus: kingship acknowledged, glorified, functioning publicly. That is not yet the state of the world, and the volume of the line says so.

Kingship as the missing term

This maps onto the whole architecture. Chochmah — knowing — is available. Malchus — the world organised around what is known — is not. The gap between the two is exactly the gap between the present and the era the sources describe, and it is the gap Moshiach closes.

Your kingship is a kingship of all worlds. Present tense, stated in a prayer said three times daily by a people for whom it has not been visibly the case for two thousand years. The tradition does not resolve that tension and does not pretend to.

What changes

Nothing about the sentence changes in the Messianic era. It is already true; that is why it is already said. What changes is the register — a truth currently held in an undertone becomes the ordinary description of how things visibly are.