These three holy hierarchs, by their clear teaching of the One True Faith, defended the Church from heresies in their own time. St. Photius, on the left, was renowned for his encompassing knowledge both of secular and Divine things. He became Patriarch of Constantinople in a.d. 858 and resisted the false teachings and innovations in Trinitarian doctrine and the Creed, dying in a.d. 895.
St. Mark of Ephesus, in the center, was the only champion of the Orthodox Faith at the Counsel of Florence in a.d. 1439, when the pressures of imminent capture of Constantinople led their Patriarch and other bishops to sign a false union for the promise of military help, which never came. The people unanimously rejected this as a false council when the bishops returned, and praised St. Mark for his courageous stand for truth. He died in a.d. 1445.
St. Gregory Palamas (a.d. 1296-1359) correctly taught how we can know God directly through the interior practice of Hesychast Prayer, and by beholding the Uncreated Light of God. This resisted the innovative teaching of Thomism from the West, and St. Gregory’s teaching was confirmed in two local councils.