The Beheading of St. John the Forerunner is commemorated on August 29 in the Orthodox calendar.
St. John is mentioned in all four Gospels and is the prophesied herald of the coming of the Messiah. Scripture scholar Jaroslav Pelikan notes that St. John is a significant person in the Scriptures:
“John the Baptizer and Forerunner was, together with Mary the Theotokos, the principal sign of the continuity and the transition from the covenant with Israel to the new covenant.” (Brazos Theological Commentary on the Bible: Acts, p 156)
The Hymn for the Feast Day:
The memory of the righteous is celebrated with hymns of praise, but the Lord’s testimony is sufficient for you, O Forerunner. You were shown in truth to be the most honorable of the prophets, for you were deemed worthy to baptize in the streams of the Jordan Him whom they foretold. Therefore, having suffered for the truth with joy, you proclaimed to those in hell God who appeared in the flesh, who takes away the sin of the world, and grants us great mercy.
In Orthodox tradition, not only does St. John herald the coming of the Messiah in the world, in that he also preceded Christ in death to enter Hades, the place of the dead, he was the first to announce to the dead the coming of the Messiah.