During the reign of Emperor Theodosius II (402–450), Constantinople endured nearly four months of severe earthquakes. Many buildings, including churches, homes, and sections of the city's stone walls, collapsed or were destroyed. The entire population was gripped by fear. In response, Patriarch Proclus (commemorated on November 20) led a barefoot procession with the Cross, offering fervent prayers for God's protection.

During the procession, the tremors intensified. Suddenly, a young boy from the crowd was miraculously lifted into Heaven by an unseen force, while the people cried out, "Lord, have mercy." When the child returned, he reported that he had heard angels singing, "Holy God, Holy Mighty, Holy Immortal, have mercy on us," and that a divine voice had instructed him to tell Patriarch Proclus that the people should pray using these exact words, without any additions.

Following this message, the Patriarch had the people chant the hymn. As they did, the earthquakes ceased, and the boy peacefully passed away. From that time on, the hymn was incorporated into the Divine Liturgy, exactly as it had been sung during the earthquake—and it continues to be sung to this day.