Why do people put Christmas lights up on their houses?
Because light is a symbol of Jesus The Light. Whoever follows the Light shall not walk in darkness.
Then spake Jesus again unto them, saying, I am the light of the world: he that followeth me shall not walk in darkness, but shall have the light of life. (John 8: 12)
Christmas was the moment of the Light coming into the world.
That was the true Light, which lighteth every man that cometh into the world. (John 1: 9)