He that loveth not (ho mē agapōn). Present active articular participle of agapaō “keeps on not loving.”
Knoweth not God (ouk egnō ton theon). Timeless aorist active indicative of ginōskō, has no acquaintance with God, never did get acquainted with him.
God is love (ho theos agapē estin). Anarthrous predicate, not hē agapē. John does not say that love is God, but only that God is love. The two terms are not interchangeable. God is also light (1Jo 1:5) and spirit (Joh 4:24).