Jamieson, Fausset and Brown on 1 Peter 3:9

9. evil--in deed.

railing--in word.

blessing--your revilers; participle, not a noun after "rendering."

knowing that--The oldest manuscripts read merely, "because."

are--Greek, "were called."

inherit a blessing--not only passive, but also active; receiving spiritual blessing from God by faith, and in your turn blessing others from love [Gerhard in Alford]. "It is not in order to inherit a blessing that we must bless, but because our portion is blessing." No railing can injure you (1Pe 3:13). Imitate God who "blesses" you. The first fruits of His blessing for eternity are enjoyed by the righteous even now (1Pe 3:10) [Bengel].