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:
Unto love of the brethren, or, Unto brotherly love. He briefly reminds us what God especially requires in our life, and the mark to which all our endeavors should be directed. So Paul in Ephesians 1:4 the Epistle to the Ephesians, when speaking of the perfection of the faithful, makes it to consist in love. And this is what we ought the more carefully to notice, because the world makes its own sanctity to consist of the veriest trifles, and almost overlooks this the chief thing. We see how the Papists weary themselves beyond measure with thousand invented superstitions: in the meantime, the last thing is that love which God especially commends. This, then, is the reason why Peter calls our attention to it, when speaking of a life rightly formed. 