Christmas is one of the most important days of the Church year, second only to Easter itself. Celebrating the birth of the Lord Jesus Christ, it is the culmination of the mystery of the incarnation, the feast of God becoming flesh (the Latin "in carne" means "enfleshment"). It is a uniquely Christian teaching, the Divine choosing to become one of us. Because of this belief, God is not only Transcendent, but also wholly Immanent, Emmanuel (God-with-us).
While remaining Transcendent (meaning we must rise above our present condition to reach Him), He is at the same time Immanent (meaning He is with us as we rise toward Him). Every Eucharist is like Christmas where the bread and wine are transformed into His flesh, His Body and Blood, and, in a sense, He is born anew on the altar.
The liturgical season of Christmas begins with the vigil Masses on Christmas Eve and concludes on the Feast of the Baptism of the Lord. During this season, we celebrate the birth of Christ into our world and into our hearts and reflect on the gift of salvation that is born with him, including the fact that he was born to die for us.
The Christmas tree and the Nativity scene are popular symbols of the season and a tradition in many Christian homes. It is also traditional to exchange Christmas gifts with family and friends to honor God the Father's gift of his only son to the world. Having received the gift of Christ, we naturally want to pass that gift along to our loved ones.