John 4:8 is scripture about faith that goes beyond doing to feeling God's love.
He who does not love does not know God, for God is love."
Try explaining to someone how you know when you are in love. It's the same thing when you're talking to a non-believer about God.
John 4:8 connects the dots with this verse about knowing God through love and knowing love through God. Not an easy concept, but one that rings true.