A.T. Robertson Commentary 1 John 4:7

"Beloved, let us love one another: for love is of God; and every one that loveth is begotten of God, and knoweth God." — 1 John 4:7 (ASV)

Of God (εκ του θεου). Even human love comes from God, "a reflection of something in the Divine nature itself" (Brooke). John repeats the old commandment of 2:7f. Persistence in loving (present tense αγαπωμεν indicative and αγαπων participle) is proof that one "has been begotten of God" (εκ του θεου γεγεννητα as in 2:29) and is acquainted with God. Otherwise mere claim to loving God accompanied by hating one's brother is a lie (2:9-11).