From ancient times, from the Jerusalem typicons and the constitution of the great family of Saint Sava the Sanctified, the Church has received that on the first day after the Annunciation of the Most Holy Virgin Theotokos, the Council of the Holy Archangel Gabriel, the herald of joy, is celebrated. For it is fitting to pay homage in a worthy manner to one who serves the mystery of our salvation, bringing to the Most Pure Virgin the news of the Incarnation of God the Word in her immaculate womb. When all the citizens of a city show great respect to the envoy of the earthly king who brings to the city some gracious word from the emperor, all the more so should the envoy of the Heavenly King, the wonderful Prince of Angels, who brought the all-merciful news of eternal salvation to the entire human race, be honored with a special feast. How notable is this messenger who had previously indicated his dignity to Saint Zechariah, saying: I am Gabriel, who stand before God (Luke 1:19), that is, I stand closer to the throne of God than the other Angels. And just as in the earthly kingdom the dignitary who is closest to the king has more prestige than the other dignitaries who stand further away, so in the heavenly kingdom: the holy Angels who stand closer to God and closely observe the mysteries of God, shine with greater glory and prestige than the other Angels who are in lower ranks.
https://svetigora.com/kalendar-za-8-april-6/