Even in the garden of Eden, the necessity of the birth of Christ became apparent. Though Adam and Eve walked with God in purity for a short time, one sin destroyed their close relationship. Adam's and Eve's hearts became sinful and they had to be separated from God.
From that time on, sin's presence in the heart of man kept him from having a close relationship with God. Man became so evil that God destroyed them all except Noah and his family. Though God later sent a book of rules to remind people to do right, they continued to fall back into sin and degradation.
God had a plan that would redeem his people, bringing them back to a right relationship with Him and making them pure, just as Adam and Eve had been before the first sin. Jesus, God's Son, would come to earth in the form of a human being and sacrifice his life in order to save people from sin; that they might be forgiven of their sins and thereafter live a sin-free, holy life.
First, Mary's relatives were notified by the angel that they would have a son named John. This son would prepare the way for Christ's ministry, teaching people that their sins could be purged. Then, the angel announced to Mary that she would become the mother of the Son of God. From there, a succession of events - Mary's visit with her cousin, Elizabeth, the command to return to the city of one's ancestry to be taxed, the journey to Bethlehem, the arrival at a humble stable - led to birth of Christ, the Savior of the world.
Angels heralded the birth of Jesus to certain humble shepherds. A star proclaimed to the wise men the arrival of a newborn king. And as Mary and Joseph visited the temple to bring the offering for their first born son, Simeon and Anna spoke of Christ's future ministry and redemption of souls from the power of sin.
Because of Christ's birth, life, death, and resurrection, salvation from sin was secured for all mankind.
"For unto us a child is born, unto us a son is given..." Isaiah 9:6