It is a celebration for the father of John the Baptist as God fulfills a prophecy. According to the Old Testament prophets, a herald would announce the coming of the Messiah. As Zechariah indicates, this prediction was fulfilled with the birth of John. The prior verses explicitly stated that John's role was to announce the arrival of the Promised One. Jesus is the Promised One, the Most High. 
Over the centuries, Israel had been plagued by spiritual darkness; however, at last, the people who had been walking in the dark saw a great Light shining from the sky, and the radiance of God was at last dawning on those living in the shadow of death. It is only through the face of the Lord Jesus Christ that we can see the reviving light of the knowledge of God's glory, for He is the Dayspring from above. His uniqueness is unparalleled in history.
There is no doubt that Jesus Christ is the Morning Star. Through the glorious gospel of saving grace, the Light and Life of Jesus continue to shine abroad for all who believe in His name. To a world that is engulfed in darkness, let us share the good news of the gospel so that many may come to know Jesus and be saved.

Dear Heavenly Father, Your first act of creation was to bring light into the world. In this world of darkness and despair, You brought forth light through Your Son, Jesus Christ, shining a light of hope for the world. How glorious and mighty is Your name for sending the Dayspring to be my Saviour, my Lord, My Light in a world of darkness, and our Life. Thank You so much for the blessings You have bestowed on each of us.
In Jesus's name I pray. Amen.