He that loveth not (ο μη αγαπων). Present active articular participle of αγαπαω "keeps on not loving."

Knoweth not God (ουκ εγνω τον θεον). Timeless aorist active indicative of γινωσκω, has no acquaintance with God, never did get acquainted with him.

God is love (ο θεος αγαπη εστιν). Anarthrous predicate, not η αγαπη. John does not say that love is God, but only that God is love. The two terms are not interchangeable. God is also light (1 John 1:5) and spirit (John 4:24).