The wise men stepped from the shadows and were deemed to be three in number, each one a mighty king who knelt in turn to pay homage and present his gift to the greatest king of all. (Matthew 2:1–2)
Epiphany, also known as Three Kings’ Day, is a Christian feast day that celebrates the revelation of God in his Son as human in Jesus Christ. The traditional date for the feast is January 6. However, since 1970, the celebration is held in some countries on the Sunday after January 1. In Western Christianity, the feast commemorates principally (but not solely) the visit of the Magi to the Christ child, and thus Jesus’ physical manifestation to the Gentiles. Moreover, the feast of the Epiphany, in some Western Christian denominations, also initiates the liturgical season of Epiphanytide. Eastern Christians, on the other hand, commemorate the baptism of Jesus in the Jordan River, seen as his manifestation to the world as the Son of God.
Pope Benedict explains: It is hard to say how far back the beginnings of the Christmas feast go. It assumed its definitive form in the third century. At about the same time the feast of the Epiphany emerged in the East on January 6 and the feast of Christmas in the West on December 25. The two feasts had different emphases because of the different religious and cultural contexts in which they arose, but essentially their meaning was the same: the celebration of the birth of Christ as the dawning of the new light, the true sun, of history. Eventually, however, the emphasis on January 6 shifted--particularly in the west (and in some parts of the east)--to reflect manifestations of Christ beside that which occurred at his birth (namely, those that occurred at the coming of the magi, at his baptism, and at the wedding feast of Cana).
Source: The Holy Bible | wikipedia.org