The Word became flesh and has made his dwelling among us. We have seen his glory. The essence of Christmas is God deciding to assume our creaturely nature in order to dwell in our midst (cf. John 1:14). This is the meaning of Christmas in simple terms. And while this is a fact that remains unrefuted, there has not been a shortage of interpretations as to why God chose, at one point in time, to make a dwelling with his creation. Among the various classic interpretations to the fact of God assuming a creaturely nature is that of St. Anselm of Canterbury, a theologian who lived in the 11 ^thcentury AD. In his work titled  Cur Deus Homo (why God became man), St. Anselm reasons that God was “forced” by circumstances (the fall of Adam and Eve from grace) to assume a creaturely nature. The implication is that had Adam and Eve not fallen from grace, God would not have come to dwell with us. In other words, while God coming to dwell amongst his creatures is itself a wonderful thing, it was nonetheless occasioned by a  misdeed, so to speak. However, not all Christian thinkers subscribe to this  Anselmian interpretation.
Those who do not accept the foregoing  Anselmian interpretation hold that God coming to dwell in our midst was not a mere  accident or a consequence of a  happy fault (as the rebellion of Adam and Eve has come to be known) . Rather, God coming to dwell with his creation had been part of the creative plan of God from the very beginning. God had planned that in the  fullness of time,God was to assume our nature in order to bring to culmination the creative process. To us members of the Christian faith, that  fullness of time took place over two thousand years ago when the Son of God was born as one of us (cf. Gal 4:4). Moreover, as the Second Reading from the Letter to the Hebrews reminds us, it is an event that marked a very important phase in the history of God’s relationship with his creation. In Jesus Christ, God’s relationship to creation has been, as it were, personalized. 
God becoming a human person breaks all the barriers that stood between God and human beings. In Jesus Christ God made man, God descends from the heavens in order to interact with us as one of us. In Jesus Christ, God assumes human nature in its fullness- both our weaknesses and strengths, and as such is able to relate to us as one who understands our situation (Jesus lived like us in all things but sin). In Jesus Christ, all that men and women only used to hear said about God is concretized and made visible. If God used to be known as a loving and compassionate God, Jesus enables us to experience that in how he was ready to embrace the disenfranchised and provide for those who came to him even if it meant rubbing shoulders with the religious leaders. If God was known to be a giver of second chances, we experience that in the way Jesus forgave sinners like Zacchaeus and the repentant thief. Jesus enables us to experience God in fullness. 
We celebrate Christmas because we have experienced God made human in our lives. We celebrate Christmas because we have experienced the forgiveness of God in Jesus Christ. We celebrate Christmas because we have experienced God healing us and providing for us in Jesus Christ. And as we thank God for this great feast, we are also reminded to embody the good things we have got from God and like Jesus, enable others to experience the love and goodness of God through us.