Albert Barnes Commentary Zechariah 12:5

"And the chieftains of Judah shall say in their heart, The inhabitants of Jerusalem are my strength in Jehovah of hosts their God." — Zechariah 12:5 (ASV)

And the princes of Judah - He pictures the onemindedness of the Church. No one will assume anything for himself; each will exalt the strength which the other was to him; but all, "in the Lord." The princes of Judah will say in their heart, not outwardly or politically, but in inward conviction, Strength to me (all speak as one) are the inhabitants of Jerusalem in the Lord of hosts their God.

The highest in human estimation acknowledge that their strength is in those who are of no account in this world; in fact, the hearts of the poor are always the strength of the Church; but that strength is "in the Lord of hosts"; in Him, in whose hands are the powers of heaven and earth, in contrast to the petty turmoil on earth. God had chosen Jerusalem (Zechariah 1:17; Zechariah 2:12; Zechariah 3:2); therefore she was invincible. That most glorious prince of Judah, Paul, said, I can do all things in Christ who instrengthens me.