Saint Isaac lived during the IV century, received the monastic tonsure and pursued ascetic labors in the desert. During the reign of Emperor Valens (364-378), a zealous adherent of the Arian heresy, there was a persecution of the Orthodox, and churches were closed and destroyed.
Hearing of the persecution, Isaac left the wilderness and went to Constantinople to console and encourage the Orthodox, and to fight against the heretics. At that time, barbarian Goths along the Danube River were making war against the Empire. They seized Thrace and advanced toward Constantinople.
When Emperor Valens was leaving the capital with his soldiers, Isaac cried out, “Emperor, reopen the churches of the Orthodox, and then the Lord will aid you!" But the Emperor, disdaining the Saint's words, continued confidently on his way. The Saint repeated his request and prophecy three times. The angry Emperor ordered Saint Isaac to be thrown into a deep ravine, filled with thorns and mud, from which it was impossible to escape.
Isaac remained alive by God’s help, and when he emerged he overtook the Emperor and said, “You wanted to destroy me, but three Angels pulled me from the mire. Hear me, reopen the churches for the Orthodox and you shall defeat the enemy. If you do not heed me, then you shall not return. You will be captured and burnt alive.” The Emperor was astonished at the Saint's boldness and ordered his attendants Saturninus and Victor to seize him and hold him in prison until his return.
Isaac’s prophecy was soon fulfilled. The Goths defeated and pursued the Greek army. The Emperor and his Arian generals took refuge in a barn filled with straw, and the attackers set it ablaze. After news of the Emperor's death was received in Constantinople, Isaac was released and honored as a prophet.
Then the holy Emperor Theodosios the Great (379-395) came to the throne. On the advice of Saturninus and Victor, he summoned the Elder, treating him with great respect. Obeying his instructions, he banished the Arians from Constantinople and restored the churches to the Orthodox. Isaac wanted to return to his desert, but Saturninus and Victor begged him not to leave the city, but to remain and protect it by his prayers.
Saturninus built a monastery for Isaac in Constantinople, where monks gathered around him. Isaac was the Monastery’s abbot and spiritual guide. He also nourished laypeople, and helped many of the poor and suffering.
When he had reached an advanced age, Isaac made Dalmátos the next abbot. The Monastery was later named for Dalmátos.
Saint Isaac reposed in the year 383.
Appearing as an example of abstinence, and a support of the Church,
O Isaac, adornment of the Fathers, your life was radiant with virtues,
and you clearly expounded the word of Orthodoxy.
O Venerable Father, entreat Christ God that He may grant us great mercy.
As a faithful servant of God,
you were inflamed with zeal for the Church of Christ,
holding the reins of the Emperor Valens,
you prophetically foretold His death in a fire
because of his closure of the churches.
Therefore, always pray for us who honor you,
O Venerable Father Isaac.