In 1618, after living as a monk for nearly fifteen years, he was appointed to be archbishop of the Eastern Rite Diocese of Polotzk, and he devoted his energies to work for the reunion of the Church, all the while deepening the faith of his people through his preaching and his example. There were those in the Orthodox Church, not in union with Rome, who were very much against his work towards unity, and a group of them decided he must be stopped, making plans to assassinate him. In fact, St. Josaphat knew there were many who did not want unity, and he knew his life was in danger; however, he pressed forward in his work to heal the rift between East and West.
One day when he was visiting part of his diocese in territory which is now in Russia, his enemies made an attack on the place where he was staying, and many of those who were traveling with St. Josaphat were killed. Quietly and with humility, St. Josaphat went toward the attackers and asked them why they had done such a thing, saying to them, “If you have something against me, see, here I am.” The crowd screamed at him saying, “Kill the papist!” They ran towards him with their weapons, killing him with an axe-blow to his head.
St. Josaphat's body was thrown into the river, but it remained on the surface of the water, surrounded by rays of light, and was recovered. Those who had murdered him, when they were sentenced to death, repented of what they had done. Through the gentle example of St. Josaphat and helped by his heavenly intercession, through the grace of God they became Catholics.
Raise up, O Lord, we pray thee, in thy Church the Spirit whereby Saint Josaphat thy martyr and bishop laid down his life for the sheep: That by his intercession, we, being moved and strengthened by the same, may not fear to lay down our lives for our brethren; through Jesus Christ thy Son our Lord, who liveth and reigneth with thee, in the unity of the same Holy Spirit, ever one God, world without end. Amen.