Jamieson, Fausset and Brown on 1 Peter 2:21

21. Christ's example a proof that patient endurance under undeserved sufferings is acceptable with God.

hereunto--to the patient endurance of unmerited suffering (1Pe 3:9). Christ is an example to servants, even as He was once in "the form of a servant."

called--with a heavenly calling, though slaves.

for us--His dying for us is the highest exemplification of "doing well" (1Pe 2:20). Ye must patiently suffer, being innocent, as Christ also innocently suffered (not for Himself, but for us). The oldest manuscripts for "us ... us," read, "you ... for you." Christ's sufferings, while they are for an example, were also primarily sufferings "for us," a consideration which imposes an everlasting obligation on us to please Him.

leaving--behind: so the Greek: on His departure to the Father, to His glory.

an example--Greek, "a copy," literally, "a writing copy" set by masters for their pupils. Christ's precepts and sermons were the transcript of His life. Peter graphically sets before servants those features especially suited to their case.

follow--close upon: so the Greek.

his steps--footsteps, namely, of His patience combined with innocence.