This is a metaphor which means "the character of God is love." See how you translated this in [1 John 4:8](../04/08.md). (See: [[rc://en/ta/man/translate/figs-metaphor]])
To remain in someone means to continue to have fellowship with him. See how you translated "remains in God" in [1 John 2:6](../02/06.md). Alternate translation: "continues to have fellowship with God, and God continues to have fellowship with him" or "stays joined with God, and God stays joined with him" (See: [[rc://en/ta/man/translate/figs-metaphor]])