This passage confuses me a bit, not the part about those who love no do not know God.. but the phrase " God is love.". I thought God is God. Not long ago I settled in my mind the meaning of this passage "God is love.". The context for understanding comes from 1 John 4:3

"Every spirit that does not confess Jesus Christ in the flesh having come of God is not and this is that of the Antichrist which he have heard that it doeth come and now in the world it is already."

Then

"You are of God, little children and you have overcome them because greater is he who is in you than he who is in the world."

The context is still speaking of contrasting spirits, the SPIRIT of God and the SPIRIT of Antichrist. The SPIRIT of truth and the SPIRIT of error. "You are [of THE SPIRIT] of God..."

"Beloved, may we love one another, for love is [of the SPIRIT] of God and everyone who loves is born of God and knows God. He who does not love does not know God, for [the Spirit of] God is love."

AMEN and AMEN!