He came to what was his own, and his own people did not accept him. But to all who received him, who believed in his name, he gave power to become children of God, who were born, not of blood or of the will of the flesh or of the will of man, but of God. This is the Christmas story. Truly, this is the greatest of mysteries. The concept of God appearing in human form is not unique to Christianity.
Ancient mythology is replete with stories of gods who took on the form of men.
The Hebrew scriptures contain many descriptions of an anthropomorphic Yahweh. You may recall the story of how Abraham was seated under the Terebinths of Mamre when three men appeared to inform him of the imminent birth of his son, Isaac. The story implies that two of the men were angels and one was God himself. That is, God appeared in human form. Abraham and Yahweh had a conversation about the destruction of Sodom and then God disappeared.