1 Peter 2:25 For ye were as sheep going astray; but are now returned unto the Shepherd and Bishop of your souls.
Hebrews 13:20 Now the God of peace, that brought again from the dead our Lord Jesus, that great shepherd of the sheep, through the blood of the everlasting covenant,
1 Peter 5:4 And when the chief Shepherd shall appear, ye shall receive a crown of glory that fadeth not away.
Acts 20:28 Take heed therefore unto yourselves, and to all the flock, over the which the Holy Ghost hath made you overseers, to feed the church of God, which he hath purchased with his own blood.
Christ is the Chief Shepherd, the Great Shepherd, and the Bishop of our souls.
Now, in Acts 20:28 Paul addresses the elders of pastors of the church at Ephesus and tells them to feed the church of God, that is to say, the local church at Ephesus. These elders where under-shepherds. They were directly responsible to the Great Shepherd as they were to feed the sheep in Ephesus that God had given to them. Those sheep were called their "flock" in Ephesus.
Note again:
Acts 20:17 And from Miletus he sent to Ephesus, and called the elders of the church.
--That gives vs. 28 in context. He was speaking to the elders (pastors) of the church at Ephesus.