This is a rhetorical question, with the implicit answer “No one.” You is plural, referring to all the readers of the letter. Harm is the verbal form of evil in verse 12 (kakos—kakeō), which makes the transition from verse 12 to 13 much less abrupt in the Greek; the last word in verse 12 becomes a point of departure to verse 13 and following (compare Biblia Dios Habla Hoy “who can do you evil”). Harm describes in a general way any kind of injury (Phillips “injure”) or mistreatment (Moffatt “wrong”; Jerusalem Bible “hurt”), but here is used in a special sense of permanent injury, or perhaps injury in a spiritual sense, that is, affecting their faith adversely. Christians do not escape persecution and difficulties by doing good; in fact the opposite may be closer to the truth: they are persecuted simply because they are eager to do good. But in the long run, such persecutions do not do them permanent harm, and do not affect adversely their faith and commitment to God, or their proper attitude towards others, especially to non-Christians. It is possible that Peter has in mind specific groups or individuals who are the source of harm; but it is more likely that the focus here is not on who does the harming, but on the fact that Christians will not be harmed. Accordingly, this sense can be captured by a passive recasting of the rhetorical question, for example, “you will not be harmed if….”
Since the context does not point to any particular individual or group who are likely to harm Christians, it is possible to recast the rhetorical question as “will anyone harm you if you are eager to do what is good?” In some languages one may employ a rhetorical question, but some kind of emphatic answer must immediately follow. Therefore, one is obliged in certain instances to add the answer, namely, “no one.” Since, however, many languages do not employ rhetorical questions, but have a strong negative equivalent, the question may be recast as “certainly no one will harm you if you are eager to do what is good,” or in passive form, “surely you will not be harmed if you are eager to do what is good.”
Who will harm you may be conveniently rendered as “who will cause you to suffer” or “who will hurt you.”
Eager to do what is good is literally “zealous of the good” (compare Titus 2.14). To be “zealous” of something is to desire it, and strive for it with all one’s heart (compare New English Bible “devoted to”; New American Bible “committed deeply to”; Moffatt “a passion for”). What is good picks up a favorite theme of the letter; in this context, it connects this verse with verse 11 and 12a. For good, see 2.12; 2.15.
Eager to do what is good may be rendered as “want very much to do what is good” or “try very hard to do what is good” or “work with all your strength to do what is good.”
The rendering of good must be closely related to the rendering of right in verse 14. It is of course not necessary to translate the two expressions in the same way, but there should be sufficient overlapping of meaning so that there will not appear to be a distinct difference; otherwise, the reader might not understand the relevance of the first clause of verse 14.
Quoted with permission from Arichea, Daniel C. and Nida, Eugene A. A Handbook on The First Letter from Peter. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .