Theophany means the shining-forth of God. At the Baptism of Christ in the Jordan, the Trinity is revealed openly for the first time: the Son standing in the water, the voice of the Father naming Him the Beloved, and the Spirit descending as a dove. The Church keeps this feast as the manifestation of the one God in three Persons, not a doctrine argued but a mystery shown at the riverbank.
Christ had no need of baptism, for He was without sin. He entered the water not to be cleansed but to cleanse it, to sanctify the waters and, through them, all creation, and to go down into the Jordan as He would go down into death, that He might raise us with Him. So the feast is bound to Pascha in its meaning, a first descent that points toward the great one.
Because of this, Theophany is the day of the Great Blessing of Waters. The Church blesses water and carries it to homes, a sign that matter itself is not despised but hallowed, made again a vessel of grace. The feast falls on January 6, twelve days after the Nativity, completing the cycle of the Lord's coming.