In that day shall thy mouth be opened to him which is escaped, and thou shalt speak, and be no more dumb: and thou shalt be a sign unto them; and they shall know that I am the LORD. In that day shall thy mouth be opened - What is, When some one who shall have escaped from Jerusalem, having arrived among the captives, shall inform them of the destruction of the city, the temple, the royal family, and the people at large; till then he might suppress his tears and lamentations. And we find from Ezekiel 33:21, that one did actually escape from the city, and informed the prophet and his brethren in captivity that the city was smitten.
Thus he was not only a prophet to foretell such things, but he was also a sign or portent, shadowing them out by circumstances in his own person and family; and thus the prediction, agreeing so perfectly with the event, proved that the previous information was from the Lord.
Commentary on the Bible, by Adam Clarke [1831].