Jamieson, Fausset and Brown on Zechariah 2:5

5. I ... wall of fire round--Compare Zec 2:4. Yet as a city needs some wall, I Jehovah will act as one of fire which none durst approach (Zec 9:8; Is 26:1).

glory in the midst--not only a defense from foes outside, but a glory within (Is 60:19; Re 21:23). The same combination of "glory and defense" is found in Is 4:5, alluding to the pillar of cloud and fire which defended and enlightened Israel in the desert. Compare Elisha in Dothan (2Ki 6:17). As God is to be her "glory," so she shall be His "glory" (Is 62:3).