God in the flesh!:

"...And the angel said unto her, Fear not, Mary: for thou hast found favour with God. And, behold, thou shalt conceive in thy womb, and bring forth a Son, and shalt call His name JESUS. He shall be great, and shall be called the Son of the Highest: and the Lord God shall give unto Him the throne of His father David: And He shall reign over the house of Jacob for ever; and of His kingdom there shall be no end. Then said Mary unto the angel, How shall this be, seeing I know not a man? And the angel answered and said unto her,

...The Holy Ghost shall come upon thee, and the power of the Highest shall overshadow thee: therefore also that Holy Thing which shall be born of thee shall be called the Son of God. And, behold, thy cousin Elisabeth, she hath also conceived a son in her old age: and this is the sixth month with her, who was called barren. For with God nothing shall be impossible..."Luke 1:35-37...

Christmas is about celebrating the birth of our Lord and Saviour Jesus Christ. It was on one appointed day that the Son of God, who had existed from the beginning with God the Father, became Flesh.The Angel of the Lord gave the Good news to the shephards as reported in the Gospel of Luke:

"...And there were in the same country shepherds abiding in the field, keeping watch over their flock by night. And, lo, the angel of the Lord came upon them, and the glory of the Lord shone round about them: and they were sore afraid. And the angel said unto them, Fear not: for, behold, I bring you good tidings of great joy, which shall be to all people. For unto you is born this day in the city of David a Saviour, which is Christ the Lord. And this shall be a sign unto you; Ye shall find the babe wrapped in swaddling clothes, lying in a manger. And suddenly there was with the angel a multitude of the heavenly host praising God, and saying, Glory to God in the highest, and on earth peace, good will toward men. And it came to pass, as the angels were gone away from them into heaven, the shepherds said one to another, Let us now go even unto Bethlehem, and see this thing which is come to pass, which the Lord hath made known unto us. And they came with haste, and found Mary, and Joseph, and the Babe lying in a manger. And when they had seen it, they made known abroad the saying which was told them concerning this child..." (Luke 2:8-17)