Jamieson, Fausset and Brown on 1 Peter 3:8

8. General summary of relative duty, after having detailed particular duties from 1Pe 2:18.

of one mind--as to the faith.

having compassion one of another--Greek, "sympathizing" in the joy and sorrow of others.

love as brethren--Greek, "loving the brethren."

pitiful--towards the afflicted.

courteous--genuine Christian politeness; not the tinsel of the world's politeness; stamped with unfeigned love on one side, and humility on the other. But the oldest manuscripts read, "humble-minded." It is slightly different from "humble," in that it marks a conscious effort to be truly humble.