Deepertruth: The Building Block that was rejected became the Cornerstone

So put away all malice and all guile and insincerity and envy and all slander. Like newborn babes, long for the pure spiritual milk, that by it you may grow up to salvation; for you have tasted the kindness of the Lord. 

Come to him, to that living stone, rejected by men but in God's sight chosen and precious; and like living stones be yourselves built into a spiritual house, to be a holy priesthood, to offer spiritual sacrifices acceptable to God through Jesus Christ. 

For it stands in scripture: "Behold, I am laying in Zion a stone, a cornerstone chosen and precious, and he who believes in him will not be put to shame." To you therefore who believe, he is precious, but for those who do not believe, "The very stone which the builders rejected has become the head of the corner," and "A stone that will make men stumble, a rock that will make them fall"; for they stumble because they disobey the word, as they were destined to do. 

But you are a chosen race, a royal priesthood, a holy nation, God's own people, that you may declare the wonderful deeds of him who called you out of darkness into his marvelous light.

Jesus is the Building Block and the reason for why Christmas is so important.  Jesus is the Light of the world who shines through the darkness.