Romans 5:11: "More than that, we also rejoice in God through our Lord Jesus Christ, through whom we have now received reconciliation."
Romans 8:32-33: "32 He who did not spare his own Son but gave him up for us all, how will he not also with him graciously give us all things? 33 Who shall bring any charge against God's elect? It is God who justifies."
John 1:14: "And the Word became flesh and dwelt among us, and we have seen his glory, glory as of the only Son from the Father, full of grace and truth."
Genesis 3:15: "'I will put enmity between you and the woman, and between your offspring and her offspring; he shall bruise your head, and you shall bruise his heel.'"
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The text is public domain:
Let our gladness have no end, alleluia!
For to earth did Christ descend, alleluia!
On this day God gave us
Christ, His Son, to save us;
Christ, His Son, to save us.
Prophesied in days of old, alleluia!
God has sent Him as foretold, alleluia!
On this day God gave us
Christ, His Son, to save us;
Christ, His Son, to save us.
See, the loveliest blooming rose, alleluia!
From the branch of Jesse grows, alleluia!
On this day God gave us
Christ, His Son, to save us;
Christ, His Son, to save us.
Into flesh is made the Word, alleluia!
He, our refuge and our Lord, alleluia!
On this day God gave us
Christ, His Son, to save us;
Christ, His Son, to save us.
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Both of the texts from Romans seem to be referenced in the refrain. "We have now received reconciliation" (from Romans 5:11) and "He who did not spare his own Son but gave him up for us all" (from Romans 8:32) both describe the same thing as "On this day God gave us / Christ, His Son, to save us." Romans 5:11 - specifically "we also rejoice" - might also be behind the first line, "Let our gladness have no end." It's a similar sentiment, although there isn't a resemblance as far a word choice.
Genesis 3:15 is cited although there aren't phrases in the hymn that resemble it. I think this verse, specifically "he shall bruise your head," is listed for the source of the lines "Prophesied in days of old" and "God has sent Him as foretold," although those lines could easily refer to a number of other Bible verses.
John 1:14 is the source for the first line of the fourth verse: "Into flesh is made the Word."
"The loveliest blooming rose... from the branch of Jesse" in the third verse comes from (the un-cited) Isaiah 11:1: "There shall come forth a shoot from the stump of Jesse, and a branch from his roots shall bear fruit."
