Adam Clarke on 1 Peter 3:14

But and if ye suffer - God may permit you to be tried and persecuted for righteousness' sake, but this cannot essentially harm you; he will press even this into your service, and make it work for your good.

Happy are ye - This seems to refer to Mat 5:10, etc. Blessed or happy, are ye when men persecute you, etc. It is a happiness to suffer for Christ; and it is a happiness, because if a man were not holy and righteous the world would not persecute him, so he is happy in the very cause of his sufferings.

Be not afraid of their terror - Τον δε φοβον αυτων μη φοβηθητε· Fear not their fear; see Isa 8:12. Sometimes fear is put for the object of a man's religious worship; see Gen 31:42; Pro 1:26, and the place in Isaiah just quoted. The exhortation may mean, Fear not their gods, they can do you no hurt; and supposing that they curse you by them, yet be not troubled; "He who fears God need have no other fear."