A.T. Robertson Commentary 1 Peter 3:13

"And who is he that will harm you, if ye be zealous of that which is good?" — 1 Peter 3:13 (ASV)

That will harm you (ο κακωσων υμας). Future active articular participle of κακοω, old verb (from κακος, bad) as in Ac 7:6,19. Any real hurt, either that wishes to harm you or that can harm. See the words in Isa 50:9.

If ye be (εαν γενησθε). Rather, "if ye become" (condition of third class with εαν and second aorist middle subjunctive of γινομα).

Zealous of that which is good (του αγαθου ζηλωτα). "Zealots for the good" (objective genitive after ζηλωτα (zealots, not zealous), old word from ζηλοω (1 Corinthians 12:12).