Irenaeus was educated by one of the apostolic fathers, Polycarp who was a sincere disciple of Apostle John according to Christian tradition. His name is remembered in our history as one of the founding fathers of the modern era foreign missionary as his journey to spread Christianity reached to the western area, Lyon, from the Eastern Orthodox Church. He criticized Gnosticism, which proclaimed the most important theme in Christianity is just spiritual elements and that it does not give any value to our daily struggles such as our bodily life and materialistic world. Gnosticism fiercely challenged the Christian leaders of the day with their own special school of thought. The followers of Gnosticism, however, failed to simplify their complex system of thoughts and further declined to synthesize the scattering religious thoughts. And they took the separation of real world and spiritual world to the extreme. Some point out that the followers of Gnosticism lived near brim of the river, Euphrates, where Judaism and Christianity were both taught, and this could have led them to have a skewed understanding of the Bible. In that point, Gnosticism came short on comprehending the Word completely and chose the parts that complied with its intentions. As a result, it never had the true understanding of the Bible. Irenaeus, on the other hand, observed that the history of Salvation of God is going to be coherently continued from the creation of the world to the ending time as Old and New Testament write in the complete Bible. He also believed that the fulfillment of the prophesy about the Messiah and Jesus Christ will play a part in continuing the history of God. He was able to come to theses conclusions because he saw the Bible as a whole. “Whole Bible is going to be unified as one wholly, Holy Spirit is being grasped and binded one as if it is a kind of chain. One by one united and somebody lift up one verse of Bible also simultaneously the other verse is following after it” According to the judgment of Irenaeus, if somebody accepts and believes in the perfection of God, he has to acknowledge that it is illogical to have an insufficient view of the Bible. He admits that the Bible is the gift of God for humanity. His position on this matter justifies him to speak for the authority of the Bible. Upon understanding the place of the Bible in the real world, Irenaeus claimed that salvation of the material world is as important as salvation of the humanity. Before discussing the doctrine of Christ, it is important to clarify why the Gnostics’ view was dangerous. Originally, they believed that life in flesh was meaningless, therefore, it was inevitable for them to reject the idea of incarnation of the Christ. Furthermore, they could not agree that a divine being could face death on the cross. In fact, they endeavored to introduce the two sons theory which states that the divine Christ left His flesh on the cross, therefore only the flesh faced death. Irenaeus, however, never spoke lowly of Christianity which obviously did not believe in the two sons theory, and believed that Creator in Old Testament is the same God who is revealed as Father in New Testament. This, once again, conflicted against the Gnostics’ belief that Creator in Old Testament is different from God in New Testament. Irenaeus later pointed out that God and Son of God consist of same essence that is Homoousios. When Markus Aurelius was the emperor of Rome for 19 years(161～180 ca.), Bishop Irenaeus of Lyon had protected the Church with the spirituality of martyrdom. Also he had strengthened the theological system confronting the challenges of Gnosticism. Traveling throughout and outside the empire, Irenaeus truly lived the life of the brilliant leader, serving for the Church of God successfully.