The following is an excerpt from “The Reformed View” by Sinclair Ferguson:

When Peter urges slaves to live as Christians, he tells them: “Christ suffered for you, leaving you an example, that you should follow in his steps” (Pet. 2:21). Peter is applying to slaves a general principle which governs all Christian living. His language is graphic: example (hupogrammos, or “write under”) is the word for a written copy. It belongs to the world of elementary education, where the teacher writes
letters on one line and tells the child to copy them on the next line. Peter is urging Christians to write the biography of their own lives with one eye on the lifestyle which Jesus had written. Imitation of the incarnate Savior is the essence of continuing sanctification.