“The third part burnt in the midst of the city” represents those who perished within the city during the siege; “the third part smitten about it” (the city) “with” the sword, those who were killed about the city during the same period: “the third part scattered to the wind” those who after the siege were dispersed in foreign lands.
In the midst of the city - The prophet is in exile, and is to do this in the midst of Jerusalem. His action being ideal is fitly assigned to the place which the prophecy concerns.
When the days of the siege are fulfilled - i. e., “when the days of the figurative representation of the siege are fulfilled.”