“He that loveth not knoweth not God; for God is love.”
1 John 4:8

The word of God leaves no doubt as to how we can vet the man who knows God, there are no grey areas, he puts it succinctly, the one who loves knows God:
“…every one that loveth is born of God, and knoweth God.” 1 John 4:7
The one who doesn’t love, doesn’t know God.
He repeats it twice to make clear that there is no other way to determine who knows God.
He could have said, the man who understands or talks about love, understands or knows God, but that’s not what he said because if you knew God, you wouldn’t only be able to give seminars on the importance of love, but your would live a life of love. Your knowledge wouldn’t just puff you up but would influence, improve, build and transform you:
“…Knowledge puffs up, but love builds up.” 1 Corinthians 8:1, ISV

Bible Reading Plan: Deuteronomy 8 and Ephesians 1