How do we know what is genuine? John has already stated that upholding the name and the position of Jesus Christ as the Son of God is the hallmark for the genuine believer and again he now mentions the second evidence.
“Whoever claims to love God yet hates a brother or sister is a liar. For whoever does not love their brother and sister, whom they have seen, cannot love God, whom they have not seen. And he has given us this command: Anyone who loves God must also love their brother and sister.” (1 John 4 v 20-21)
It’s the proof. Loving the easier of the two (a fellow believer that you can see) is proof that you love the hardest (God you cannot see).
The hallmark of genuineness is no matter their gifting, ability and how good they may be at speaking, if you cannot see love then what you are experiencing is a lie. They are not who they say they are. They do not love God nor do they know Him.
Why is this so important? Because it is a command of Jesus.
“A new command I give you: Love one another. As I have loved you, so you must love one another.” (John 13 v 34)
“My command is this: Love each other as I have loved you. This is my command: Love each other.” (John 15 v 12, 17)
It isn’t easy. But it is the proof you are who you say you are and it is the obedience that Jesus demands.