One of the most moving and powerful moments of the Paschal Midnight Vigil is a custom done in many areas of Greece and few places elsewhere following the singing of "Christ is Risen". Traditionally the Gospel reading of the Resurrection prior to the singing of "Christ is Risen", as well as the initial singing of "Christ is Risen", is done outside the church. The symbolism behind this is that outside the church from Great Friday to Pascha, Hades is represented, for it was in Hades that the victory of Christ over death was first proclaimed.
The doors of the church should remain shut during this time. As the Priest or Bishop proceeds to the door to enter the church holding the Gospel book in his hands, he stops before the shut doors and begins to chant from Psalm 23 (24), while inside the shut doors of the church appropriate responses are given from the same Psalm by a Reader. This is done three times. It goes like this:
First Time
Priest: Lift up your gates, ye princes, and be ye lifted up, ye everlasting doors; and the King of Glory shall come in.
Reader: Who is this King of Glory?
Priest: The Lord strong and mighty. The Lord mighty in battle.
Second Time
Priest: Lift up your gates, ye princes, and be ye lifted up, ye everlasting doors; and the King of Glory shall come in.
Reader: Who is this King of Glory?
Priest: The Lord strong and mighty. The Lord mighty in battle.
Third Time
Priest: Lift up your gates, ye princes, and be ye lifted up, ye everlasting doors; and the King of Glory shall come in.
Reader: Who is this King of Glory?
Priest: The Lord strong and mighty. The Lord mighty in battle. THE LORD OF THE POWERS. HE IS THE KING OF GLORY.
When the priest says "Lift up your gates" ("Άρατε Πύλας") each of the three times, he is supposed to knock on the shut doors with either the Cross or the Gospel book. When he says "The Lord of the Powers" at the end, he is supposed to kick the now slightly opened yet still shut door with his feet and open them (or force it open with his hands). He then proceeds inside chanting the final verse above.
This old tradition is supposed to represent a dialogue between Christ and Hades (Death or Satan), and Christ trampling the gates of Hades, just as it is depicted in the icon of Christ's Descent Into Hades.
Though traditionally this is done during the Paschal Midnight Vigil, many others choose to do it following the Great Friday outdoor procession with the epitaphios. This practice is also done when a Bishop consecrates a new church.
Below are some historical notes by Gabriel Bertonière regarding this custom:
"In only three documents of this [Studite] tradition do we find Ps 23:9-10 in connection with the entrance into the church. Vat Gr 1537 of 1573 A.D. and the printed Horologion of Grottaferrata of 1677 A.D. indicate that immediately after the final repetition of X. A. [Christ is Risen], the hegumen (or priest in Vat Gr 1537) knocks on the door of the church with the cross three times saying Ps 23:9. Afterwards, a monk from within responds with v. 10a of the same psalm. The hegumen responds with v. 10b, opens the door, and finally all enter. A marginal note in Mess Gr 115 [Typikon of Messinis] indicates after the Royal Doors have been shut following the priest's entrance into the narthex: 'και μετά του ... λγ άρατε πύλας.'
Dmitrievskij affirms that the verses from Ps 23 were also called for in two 12th century Triodia of the monastery of Simonopetra on Mount Athos (Codices 5 and 18). These have since been destroyed by fire and we do not know whether or not they were Studite or Sabbite type books. Dmitrievskij does not specify how much of the Psalm was used.
In both Jerusalem and Sinai collections we find manuscripts which add to these Stichoi (Arise O God...) one or several verses from Ps 23 (Lift up your gates...). Sabba 311 and Sinai 1097 place these after the Doxa following the other Stichoi; HS 15, after the Synapte which follows the Doxa. The insertion of the verses from this Psalm before the initial blessing in HS 43 seems strange. Perhaps this was the only available space to place them. The use of this psalm did not gain widespread acceptance. The scribe of Sinai 1108 explicitly rejects it saying that the use vv. 7 and 8 as a dialogue between Christ and the devil seems to attribute power to the devil. It did not make its way into the printed Typikon, though it survives until the present day in certain places."
"The Historical Development of the Easter Vigil and Related Services in the Greek Church", Orientalia Christiana Analecta 193, Rome, 1972, p. 201.
Below are some video examples of how this practice is performed: