In that day shall Israel be the third with Egypt and with Assyria, even a blessing in the midst of the land:
Israel be the third - the three shall be joined as one nation.
(Even) a blessing - the source of blessings to other nations, and the object of their benedictions.
In the midst of the land - rather, earth (Micah 5:7). Judah is designed to be the grand center of the whole earth (Jeremiah 3:17).