John Wesley on 2 Peter 1:7

And to godliness brotherly kindness - No sullenness, sternness, moroseness: "sour godliness," so called, is of the devil. Of Christian godliness it may always be said, "Mild, sweet, serene, and tender is her mood, Nor grave with sternness, nor with lightness free: Against example resolutely good, Fervent in zeal, and warm in charity." And to brotherly kindness love - The pure and perfect love of God and of all mankind. The apostle here makes an advance upon the preceding article, brotherly kindness, which seems only to relate to the love of Christians toward one another.