In the Orthodox Church it is customary, on the day following the Great Feasts of the Lord and the Mother of God, to remember those saints who participated directly in the sacred event. So, on the day following the Theophany of the Lord, the Church honors the one who participated directly in the Baptism of Christ, placing his own hand upon the head of the Savior.
Saint John, the holy Forerunner and Baptist of the Lord, whom the Lord called the greatest of the prophets, concludes the history of the Old Testament and opens the era of the New Testament. The holy Prophet John bore witness to the Only-Begotten Son of God, incarnate in the flesh. Saint John was accounted worthy to baptize Him in the waters of the Jordan, and he was a witness of the Theophany of the Most Holy Trinity on the day of the Savior’s Baptism.
— Text taken from oca.org Click to read the entire article (opens in a new tab)