Jamieson, Fausset and Brown on Zechariah 12:5

5. shall say--when they see the foe divinely smitten with "madness."

Judah ... Jerusalem--here distinguished as the country and the metropolis. Judah recognizes her "strength" to be "Jerusalem and its inhabitants" as the instrument, and "Jehovah of hosts their God" (dwelling especially there) as the author of all power (Joe 3:16). My strength is the inhabitants of Jerusalem, who have the Lord their God as their help. The repulse of the foe by the metropolis shall assure the Jews of the country that the same divine aid shall save them.