Through His angel God commanded Joseph,…you shall call his name Jesus, for he will save his people from their sins. The Holy Spirit informs us through Matthew that this event revealing 
Mary’s miraculous conception and revealing God’s command to name the baby Jesus, fulfilled what Isaiah had prophesied: Behold, the virgin shall conceive and bear a son, and they shall call his name Immanuel. Matthew then translates Immanuel: God with us.
Herein we find two foundational beliefs of the Christian faith. First, that this baby would save from sin. Second, that this baby is God with us. Faith in these two realities must be divinely wrought, for who can believe that a single human could save from sin, or who could believe that God became a man. And yet these two beliefs always belong together, for who but God can save from sin? Through the prophet Isaiah God declares this reality: I am the Lord, and besides me there is no savior (43:11).
In the name Jesus (Hebrew Joshua) this dual reality of God becoming man to save us is even sharpened. Jesus is a name that basically means God saves. Devout Jewish parents would name their sons Jesus (Joshua), as a reminder that God indeed saves. This child, born of the virgin, is given the name Jesus not so much as a reminder that God saves but because He IS God who saves from sin. Thus already while in the womb the ultimate person and work of this Holy-Spirit-conceived child is clearly identified. His person: True God and True Man. His Work: Saving Mankind from Sin.
Subsumed under this command given to Joseph is Christ’s journey to the cross. The Apostle Paul would later summarize Christian preaching: We preach Christ crucified. When the angel explains, He will save His people from their sins, He is identifying the central proclamation: We angels proclaim Christ crucified.
Many Christians will celebrate Christmas with a weak understanding of the purpose of this baby. Some will go only so far as to hail Him as mankind’s ultimate example. Many will only go as far as to claim Jesus as the One who reveals God’s love as He goes about healing and caring for the sick and the outcast. Others will only go as far as to tell people that Jesus was born to teach us about God. And for some He will be recognized as a sort of ultimate Moses—another great law-giver who directs His followers to absolute obedience. Though there is a kernel of truth in each of these yet ultimately these proclaimed purposes for the Christ-child are misleading and fall far short, for in them there is very little Gospel. St. Paul in the fifteenth chapter of his first epistle to the Corinthians begins his summary of the Gospel by stating: For I delivered to you as of first importance…that Christ died for our sins (v. 3). This primary purpose of the Christ echoes perfectly the primary purpose named by the angel: He will save His people from their sins.
Thus we celebrate Christmas and share its foundational meaning by pointing people to the cross, and of course to the empty tomb. The cross is the heart of the Gospel. Indeed He was delivered up for our trespasses and raised for our justification (Romans4:25) …fulfilling the prediction, He will save His people from their sins.