Their heart cried unto the Lord, etc. "Their heart" can only mean "the heart of the people of Jerusalem." For the expression, comp. Psalms 84:2, "My heart and my flesh cry aloud to the living God." To avoid the rather startling prosopopoeia in the next clause, Thenius supposes a corruption in the group of letters rendered "wall," and attaches the corrected word to the first clause, rendering thus: "Their heart crieth unto the Lord in vain; O daughter of Zion, let tears run down," etc.
Another resource, which also involves an emendation, is that of Ewald, "Cry with all thy heart, O wall of the daughter of Zion." O wall, etc. The prosepopoeia is surprising, but is only a degree more striking than that of Psalms 84:8 and Lamentations 1:4.
In Isaiah 14:31 we find an equally strong one, "Howl, O gate." Most probably, however, there is something wrong in the text; the following verses seem to refer to the daughter of Zion. Bickell reads thus: "Cry aloud unto the Lord, O virgin daughter of Zion."
Like a river; rather, like a torrent. Give thyself no rest. The word rendered "rest" means properly the stiffness produced by cold.