Albert Barnes Commentary Zechariah 9:11

"As for thee also, because of the blood of thy covenant I have set free thy prisoners from the pit wherein is no water." — Zechariah 9:11 (ASV)

As for you also - The prophet turns from the deliverance of the whole world to the former people, addressing the sorrows they would experience along the way, and the protection God would bestow on them for the sake of Him, who, according to the flesh, was to be born of them.

“You too;” he had spoken of the glories of the Church, such as those her King, when He comes, would extend, embracing earth’s remotest bounds. He now turns to her, Israel after the flesh, and assures her of God’s continued protection, even in her lowest state.

The deliverance under the Maccabees was, like those under the judges, an image of the salvation of Christ and a preparation for it. They were martyrs for the One God and for the faith in the Resurrection, and, whether by doing or by suffering, preserved the sacred line until Christ should come.

By the blood of your covenant - Osorius says: “Not by the blood of those ancient victims, but by the blood of your covenant, will you be united to the empire of Christ, and so obtain salvation. As the Lord Himself says, This is the blood of covenant, which is shed for you.” The gifts and calling of God are without repentance (Romans 11:29). That symbolic blood, by which, fore-signifying the New Covenant, He made them His own people—Behold the blood of the covenant, which the Lord hath made with you concerning all these words (Exodus 24:8)—still endured, amid all their unfaithfulness and breaches of it.

By virtue of it, God would send forth her imprisoned ones “out of the” deep, dry “pit,” “the dungeon” in which they could be kept securely because life was not threatened . Out of any depth of hopeless misery in which they seemed to be shut up, God would deliver them.

As David says, He brought me up also out of a horrible pit, out of the miry clay, and set my feet upon a rock and established my goings (Psalms 40:2); and Jeremiah says, They have cut off my life in the dungeon, and cast a stone upon me. I called upon Your Name, O Lord; out of the low dungeon You have heard my voice (Lamentations 3:53, 3:55-56).

Augustine (City of God, Book 18, Chapter 35, section 3) says: “The dry and barren depth of human misery, where there are no streams of righteousness, but the mire of iniquity.”