O Come, O Come, Emmanuel. This is one of the most beloved of Advent hymns, and it dates back to the ninth century, to the time of Charlemagne. If you reference hymn 357 in your hymnal, you will see on the other side of the page the “O Antiphons” from which this hymn is derived, so called because each ascription to Jesus begins “O,” even in the original Latin. These “O Antiphons” are ancient, probably dating from the earliest centuries of the Church, and were typically chanted and prayed the seven days prior to Christmas Eve. (Hence, there is a date preceding each of the antiphons in the hymnal.) These were so ubiquitous it was even a legitimate question to ask one if they had “kept their Os.” You will also notice on the bottom right page of the hymnal the references from Isaiah. This hymn is meant to connect the Old Testament prophecies with their fulfillment in Jesus. Following are several:
Key of David: Isaiah 22:22: "I will place the key of the House of David on his shoulder. When he opens, no one shall shut; when he shuts, no one shall open.” In both OT and NT contexts, the key has been the traditional symbol of kingly authority. Through this “key,” the power of heaven is held or loosed. In Matt. 16: 19, Jesus states, “I will give you the keys of the kingdom of heaven; whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven.”
Rod (or “Root”) of Jesse: Isaiah 52:13, 15; 53:2: "See, my servant shall prosper...So shall he startle many nations, because of him kings shall stand speechless. ...He grew up like a sapling before him, like a shoot.” Christ is David’s descendant in that He was both genetically related to David, and He is also inheritor of both the earthly (David’s) and heavenly (God the Father’s) kingdom.
Dayspring from on High: Isaiah 9:1: "The people who walked in darkness have seen a great light. Upon those who dwelt in the land of gloom a light has shone.” Interestingly, “dayspring,” also translated as “rising dawn” or “morning star,” refers to an object which is not so luminescent in itself than it reflects a light greater than itself. This emphasizes Jesus’ divinity as a reflection of His Heavenly Father and reminds us that Jesus’ does not stand alone but with the Heavenly Father regarding our salvation.
Wisdom from the Most High: This ascription comes directly from apocryphal (not directly biblical for most Protestants) sources, although Christ as “Wisdom” is referred to in John 1:1. He is the Logos (“Word”) or Wisdom who is present with God before even the beginning of time.
Emmanuel: Isaiah 7:14: "Therefore the Lord himself will give you this sign: the virgin shall be with child, and bear a son, and shall name him Emmanuel.” “Emmanuel” means “God with us.” Christ has taken on human form so that we might relate to Him. He is not a stranger to us—He is no god who sits idly back and watches the world from afar. He was active in it in a very physical and real sense, and we should expect that He is no less involved in the world today. Christ has become one of us; but, as the other antiphons remind us, He is still Almighty God!
The mystery of Advent and Christmas is that this Almighty God became manifest in our world for our salvation. Christianity teaches that Christ is completely God and yet completely human. How can this be? The essence of our faith is that Christ somehow accomplished this for our benefit, and it is not necessarily for us to understand.