The Holy Archangel Gabriel was chosen by the Lord to announce to the Virgin Mary about the Incarnation of the Son of God from Her, to the great rejoicing of all mankind. Therefore, on the day after the Feast of the Annunciation, the day on which the All-Pure Virgin is glorified, we give thanks to the Lord and we venerate His messenger Gabriel, who contributed to the mystery of our salvation.
Gabriel, the holy Archistrategos (Leader of the Heavenly Hosts), is a faithful servant of the Almighty God. He announced the future Incarnation of the Son of God to those of the Old Testament; he inspired the Prophet Moses to write the Pentateuch (first five books of the Old Testament), he announced the coming tribulations of the Chosen People to the Prophet Daniel (Dan. 8:16, 9:21-24); he appeared to St Anna (July 25) with the news that she would give birth to the Virgin Mary.
The holy Archangel Gabriel remained with the Holy Virgin Mary when She was a child in the Temple of Jerusalem, and watched over Her throughout Her earthly life. He appeared to the Priest Zachariah, foretelling the birth of the Forerunner of the Lord, St John the Baptist.
The Lord sent him to St Joseph the Betrothed in a dream, to reveal to him the mystery of the Incarnation of the Son of God from the All-Pure Virgin Mary, and warned him of the wicked intentions of Herod, ordering him to flee into Egypt with the divine Infant and His Mother.
When the Lord prayed in the Garden of Gethsemane before His Passion, the Archangel Gabriel, whose very name signifies “Man of God” (Luke. 22:43), was sent from Heaven to strengthen Him.
The Myrrh-Bearing Women heard from the Archangel the joyous news of Christ’s Resurrection (Mt.28:1-7, Mark 16:1-8).
Mindful of the manifold appearances of the holy Archangel Gabriel and of his zealous fulfilling of God’s will, and confessing his intercession for Christians before the Lord, the Orthodox Church calls upon its children to pray to the great Archangel with faith and love.
The Synaxis of the Holy Archangel Gabriel is celebrated on March 26 (the day after Annunciation) as well as on July 13. All the angels are commemorated on November 8.
Text from oca.org
Troparion, Tone IV
O Supreme Commander of the hosts of Heaven, unworthy though we are, we ever entreat thee that by thy supplications thou dost protect us with the shelter of the wings of thine immaterial glory, preserving us who earnestly fall down and cry aloud: Deliver us from misfortunes in that thou art the commander of the hosts on high!
Kontakion, Tone II
Supreme commander of God, minister of His divine glory, leader of the angels and instructor of men: ask for us great mercy and that which is profitable in that thou art the supreme commander of the incorporeal hosts.