Seeing you have purified your souls in your obedience to the truth through the Spirit in sincere brotherly affection, love one another from the heart fervently:
Love one another from the heart fervently ... See in the introduction for Peter's fidelity in conforming his teaching to that of the Master.  This shows that Peter had not forgotten the Saviour's commandments to this very end.  Of particular interest is the word "Fervently," which may also be translated "earnestly."  Wheaton cited four usages of this word in the New Testament, here, in  1 Peter 4:8, and in  Luke 22:44, and in  Acts 12:5, the latter reference being to the prayer offered on behalf of Peter himself. "It denotes with supreme effort, `with every muscle strained.'"[59]