The phrase “straying like sheep” is lifted from Isaiah 53:6. The fact that Peter has referred so often to that Old Testament prophecy in the present context makes this present quote from the same source understandable. But there is more behind this quote. The word “straying” captures accurately what his readers had been doing. To “be subject…to every human institution” (1 Peter 2:13), including slavery, does not sit well with the inclination of the fallen human heart—and neither does the instruction to “honor everyone” (1 Peter 2:17), including the despotic master. That Peter’s readers were “straying” on this point is what necessitated the present paragraph to begin with. Hence Peter’s final allusion to Isaiah 53:1–12, with the connective word “for.”
25 For you were straying like sheep, but have now returned to the Shepherd and Overseer of your souls.