As for thee also (Jerusalem) by the blood of thy covenant - The covenant made with Abraham, Isaac, Jacob, and the Israelites in general, and ratified by the blood of many victims; until the time should come in which the Messiah should shed his blood, as typified by the ancient sacrifices.
I have sent forth thy prisoners - Those who were under the arrest of God's judgments; the human race, fast bound in sin and misery, and who by the pitifulness of his tender mercy were loosed, he dying in their stead.
As for thee also - The prophet turns from the deliverance of the whole world to the former people, the sorrows which they should have in the way, and the protection which God would bestow upon them for the sake of Him, who, according to the flesh, was to be born of them. “Thou too;” he had spoken of the glories of the Church, such as her king, when He should come, should extend it, embracing earth‘s remotest bounds: he turns to her, Israel after the flesh, and assures her of the continued protection of God, even in her lowest estate. The deliverance under the Maccabees was, as those under the judges had been, 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 thy covenant - Osorius: “Not by the blood of those victims of old, but by the blood of thy covenant, wilt thou 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, endured still, 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” wherein they could be kept securely, because life was not threatened (as in Genesis 37:24). 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” Psalm 40:2; and Jeremiah, “They have cut off my life in the dungeon, and cast a stone upon me. I called upon Thy Name, O Lord; out of the low dungeon Thou hast heard my voice” Lamentations 3:53, Lamentations 3:55-56. Augustine, de Civ. Dei. xviii. 35. 3): “The dry and barren depth of human misery, where are no streams of righteousness, but the mire of iniquity.”