Thine arm shall be uncovered. This, as in Isaiah 52:10, was the symbol of energetic action. The prophet was to be, as it were, no apathetic spectator of the siege which he was thus dramatizing, but is as the representative of the Divine commission to control and guide it.
The picture of the prophet's attitude, not merely resting on his side and folding his hands, as a man at ease might do, but looking intently, with bare outstretched arm, at the scene portrayed by him, must, we may well imagine, have added to the startling effect of the whole procedure.
We note the phrase, "set thy face," as specially characteristic of Ezekiel (here, and, though the Hebrew verb is not the same, Ezekiel 14:8; Ezekiel 15:7). The words "prophesy against it" may imply some spoken utterance of the nature of a "woe," like that of the son of Ananus (see above), but hardly, I think, a prolonged address.