For you were going astray like sheep; but are now returned to the Shepherd and Overseer{"Overseer" is from the Greek episkopon, which can mean overseer, curator, guardian, or superintendent.} of your souls.
The word "Shepherd" (poimeen) is the word "pastor" in Ephesians 4:11. It indicates one who tends herds and flocks or one who protects. A bishop (episkopes) is an overseer, one who watches over the flocks (Acts 20:28), indicating the character of the work. Our Lord is indeed watches over us; He is the Shepherd and Bishop of our souls.