I exhort you to be careful to do all things in the harmony of God, while your bishop presides in the place of God, and your presbyters in the place of the assembly of the apostles, along with your deacons, who are most dear to me, and are entrusted with the ministry of Jesus Christ, who was with the Father before the beginning of time, and in the end was revealed. Do this then, imitating the same godly conduct, pay respect to one another, and let no one look upon his neighbor after the flesh, but continually love each other in Jesus Christ. Let nothing exist among you that may divide you; but be united with your bishop, and those that preside over you, as a type and evidence of your immortality. (Epistle to the Magnesians -Ch 6, Justin Martyr, CA 130 AD)
It is clear in this epistle of Justin Martyr to the Magnesians that the threefold hierarchical role of Bishop, Priest (Presbyter), and deacon was in place by the time of his writing in the early second century. However, perhaps even more interesting than this is the reason that Justin gives the church for embracing their authority. His argument for respecting the hierarchy is that their respect serves as a type and evidence of our immortality. In other words, the gospel of Jesus, and salvation itself is presented to the world by the living relationship between the church and its hierarchs. Therefore, this means that without this structure at work in the life of the church, the gospel is damaged and salvation weakened; the threefold office is not merely an option.