Isaiah 64:1: "Oh that you would rend the heavens and come down, that the mountains might quake at your presence"
Isaiah 45:8: "'Shower, O heavens, from above, and let the clouds rain down righteousness; let the earth open, that salvation and righteousness may bear fruit; let the earth cause them both to sprout; I the LORD have created it.'"
Isaiah 40:1-2: "Comfort, comfort my people, says your God. Speak tenderly to Jerusalem, and cry to her that her warfare is ended, that her iniquity is pardoned, that she has received from the LORD's hand double for all her sins."
Luke 1:76-79: "'And you, child, will be called the prophet of the Most High; for you will go before the Lord to prepare his ways, to give knowledge of salvation to his people in the forgiveness of their sins, because of the tender mercy of our God, whereby the sunrise shall visit us from on high to give light to those who sit in darkness and in the shadow of death, to guide our feet into the way of peace.'"
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The first line of the first verse (the titular "O Savior, rend the heavens wide") comes from Isaiah 64:1.
The second and third verses seem to come from Isaiah 45:8. The rain imagery is present in the second verse in the phrases "morning dew," "Drop down, you clouds, the life of spring," and "rain down the King." The sprouting earth is in the third verse, "in flow'ring bud" and "in garb of green."
The line "When will You come with comfort strong?" in the fourth verse seems to be from Isaiah 40. The sixth verse has a stronger similarity, with "O come, lead us with mighty hand" away from sin and "to our promised land." "Comfort" and "the LORD's hand" are the specific words in common between the Isaiah 40 text and the hymn,
The fifth verse uses the imagery of the sunrise from Luke 1, calling upon God as the "Morning Star" and "radiant Sun," Luke 1 says that Jesus will "give light to those who sit in darkness and the shadow of death," and in the hymn, this dwelling in darkness is rendered as "We grope in gloom and dark of night."
