What we celebrate on Christmas is the coming down of God to earth in the person of Jesus, who was born as an infant in a lowly manger. The creator took a time out from His throne. He came down as a man – thus “God is with us.” In other words, with the birth of Jesus God dwelt with us. This is the doctrine of the Incarnation.
We, Christians, worship the God of the Jews. This God is known as Yahweh or Jehova. This God is a spirit. Thus Saint John the Evangelist says, those who worship God must worship Him in spirit and in truth. St. John wrote his evangel for the Greek speaking world. At the time Jesus was born, Greek was the lingua franca of the world.
Rome was the empire that ruled the world; Jesus was born when Augustus Caesar was the Roman emperor. To impose Roman law to the far reaches of the empire, Rome built an extensive road network. And there was peace throughout the empire. They called this pax romana.
When those three factors were in place (Greek as the universal language), the extensive road network of the Roman empire, and universal peace, God decided to come down to earth. He came in the form of a fetus, conceived in the womb of the Virgin Mary, was born as a helpless infant in an animal stable.
As a man, He was born among the poorest of the poor. When He went about to preach repentance for people to qualify to become citizens of His kingdom, the Power that be, both in Jerusalem and in Rome, opposed His preaching.
The Roman Empire felt insecure with Christ’s establishing His own kingdom. To derail His work, they nailed Him to the cross. His enemies nailed Him to the cross. He bled and died thereat. But He conquers death. On the third day, He resurrected from death. The blood that He shed on the cross was the very cleansing detergent used by God to wash away our sins.
He redeemed us from sin with His blood; He resurrected from death to give us eternal life. Salvation from sin is Christ’s gift to you and to me. This is the purpose of the Incarnation of God.