I have the joy of serving as a Bishop in the Lutheran Church (Independent Lutheran Diocese). However, it's good to appreciate that the Bible uses the words
presbyteros (from which we get the word
Priest) and
episkopos (from which we get the word
Bishop) interchangeably, which is to say that the Bible presents us with one pastoral office, which goes by different names, and one helper office, Deacon. And this twofold office, Bishops and Deacons, is also found very explicitly in the Didache, which is one of the earliest Christian writings we have outside of the Bible, and also appears in Clement and Polycarp. The third office of Bishop as something distinct and over the pastoral office is a later development. Now, for those who embrace an understanding of Holy Tradition, that's not a problem. But for those who hold that tradition must be governed by the Scriptures, God's Word, we confess one pastoral office (commonly translated as Overseer or Elder) and one helper office (Deacon), and we can see the requirements for these two offices in Paul's letter to Timothy, 1 Timothy 3:1-13.
Here's an example of how words for the pastoral office are used interchangeably:
Acts 20:17:
“Now from Miletus [Paul] sent to Ephesus and called the elders
(presbyteros) of the church to come to him. And when they
(the elders) came to him, he said to them: …”
Acts 20:28:
“Pay careful attention to yourselves and to all the flock, of which the Holy Spirit has made you overseers
(episkopos), to care for the Church of God, which He obtained with His own blood.”
It's also good to take note of who are present at the Jerusalem Council (Acts 15:6; Acts 15:22).
The twofold office is also recognised by Jerome, who writes (Letter 146 — To Evangelus): "The apostle clearly teaches that Presbyters are the same as Bishops." And: “The elders always elected one from among themselves and placed him in a higher station, calling him bishop, just as an army would make a commander for itself. The deacons, moreover, may elect from among themselves one whom they know to be active and name him archdeacon. For with the exception of ordination, what does the bishop have that the elder does not?”
Finally, I can mention that Bellarmine recognised that the Bible uses the words for the pastoral office interchangeably, which is why he appeals to later tradition. And from a Roman Catholic standpoint, that's possible, but for those who hold to the Scriptures as the supreme authority, it's not possible.
So, in our church body, we hold that the office of Bishop is the same as that of Pastor (or Priest). The pastoral office is by divine right, but the office of Bishop as a governing role is man-made, not by divine right. It's essentially the same as a Senior Pastor, Superintendent, or District President. And the reason we have this is because we see throughout the New Testament that they used their freedom in Christ to govern themselves for the sake of good order, in accordance with God's Word. So, very simply, many Evangelical church bodies hold that hierarchy is not demanded by God, but is allowed. But those who hold to a belief in Holy Tradition (which may include some Evangelical bodies) believe that hierarchy is necessary.
Put short: The Bible gives us two offices, and this is what we see in the earliest writings outside of the Bible. But the third office developed very early in church history, and for those who believe in Holy Tradition appeal to that. My objection is that the development, although early, is not early enough. It's not in the Bible.