Epiphany of the Lord

(Icon of the Lord's Baptism)

On January 6, the Eastern Orthodox Church celebrates the Epiphany of our Lord with His Baptism by John the Baptist in the Jordan (as recorded in Matt 3:13-17; Mark 1:9-11; Luke 3:21-22). The feast is so-named because not only does Jesus of Nazareth begin his earthly ministry revealing (gr. epiphania) himself as the Messiah, but God is revealed for the first time as Trinity and Jesus is identified as His Beloved Son and His Holy Spirit descends and rests upon Him. The feast is also called Theophany. 

Though it is nearly lost on us today, the significance of Christ's immersion in the waters cannot be understated, as the concept of an elemental watery chaos was linked very closely with fundamental nature of the cosmos in the ancient mindset. The following hymn (of many) shows what Christ's Baptism means for us when we are baptized:

The true Light has appeared and bestows illumination on all. Christ is baptized with us, even though He is above all purity; and thus He infuses sanctification into the water, which then becomes the purifying agent of our souls. What is seen belongs to earth; but what is understood transcends the heavens. By means of a bath comes salvation; by means of water comes the Spirit; by means of immersion does our ascent to God come to pass. How wonderful are Your works, O Lord! Glory to You.  
(From the Orthros Service of Epiphany)