Saint Isaac (May 30) was a soldier before he became a monk. After he was tonsured, he attained such a degree of spiritual perfection that he was accounted worthy of beholding divine visions.
When St Isaac heard about how the Emperor Valens had fallen into the Arian heresy and was persecuting the Orthodox Christians, he left his monastery and traveled to Constantinople to confront the emperor. At that time Valens was planning a campaign against the Goths. St Isaac tried to change the emperor’s mind several times, but was unable to convince him. He prophesied that Valens would die in flames because of his actions. The emperor ordered that St Isaac be thrown into prison, and promised to deal with him when he returned from his expedition. On August 9, 378 Valens was defeated at Adrianople and died in a fire after hiding in a barn, just as the saint had predicted.
Emperor Theodosius the Great, who had a great love for the saint, released him from prison and banned Arianism. St Isaac attended the Second Ecumenical Council (381), where he defended the Orthodox Faith against the Arian heresy.
St Isaac hoped to return to his monastic life in the wilderness, but a wealthy man built a monastery for him at Constantinople, and he became its first igumen. The monastery was later named for his disciple Dalmatus.
When St Isaac was approaching the end of his earthly life, he named St Dalmatus to succeed him as igumen. He lived to a ripe old age and reposed in the year 383.