When a baby is born, he can be held, seen, heard, touched, and kissed. We celebrate a birth because after a baby is born we can enter into a new dimension of personal relationship with that baby. We likewise celebrate the birth of Jesus because His birth made it possible for Mary, Joseph, the shepherds, the wise men, and us to become very close to Him.
Although we did not live at the time when we could see, touch, and hear Jesus physically, we can still be very close to Jesus. In fact, we can be closer than close to Jesus. By the power of the Spirit, we can be in Jesus and He in us (see Jn 17:23). We can even touch the body and blood, soul and divinity of Jesus in Holy Communion. We can receive Jesus and become one with Him (Jn 6:56). We can have a personal relationship with Jesus that is so deep that it will transform us and the whole world.
This relationship with Jesus is so powerful that those who live in His love are seen either as the best thing that has ever happened to the world or a threat to the culture of death (see 2 Cor 2:15-16). Thus, Christians are embraced as messengers of life, hope, and light, or they are attacked, persecuted, and sometimes killed (see Acts 7:57ff; Mt 10:17ff).
Love Jesus, the God-Man, and live the relationship that rocks the world.