Albert Barnes Commentary Ezekiel 4:7

"And thou shalt set thy face toward the siege of Jerusalem, with thine arm uncovered; and thou shalt prophesy against it." — Ezekiel 4:7 (ASV)

Therefore thou shalt set thy face - Or, “And etc.” i. e., direct thy mind to that subject.

Thine arm shall be uncovered - A sign of the execution of vengeance [Isaiah 52:10].