I John 4:8

knoweth not--Greek aorist: not only knoweth not now, but never knew, has not once for all known God. God is love--There is no Greek article to love, but to God; therefore we cannot translate, Love is God. God is fundamentally and essentially LOVE: not merely is loving, for then John's argument would not stand; for the conclusion from the premises then would be this, This man is not loving: God is loving; therefore he knoweth not God IN SO FAR AS GOD IS LOVING; still he might know Him in His other attributes. But when we take love as God's essence, the argument is sound: This man doth not love, and therefore knows not love: God is essentially love, therefore he knows not God.

In this chapter the apostle exhorts to try spirits (Jo1 4:1), gives a note to try by (Jo1 4:2, Jo1 4:3), shows who are of the world and who of God (Jo1 4:4-6), urges Christian love by divers considerations (Jo1 4:7-16), describes our love to God, and the effect of it (Jo1 4:17-21).

4:8 God is love, the source and embodiment of all love. This concept and the concept that “God is light” (1:5) form the foundation on which John writes this letter.