Does this approach to discernment sound cliquish - ‘Everyone who agrees with us is of the truth; everyone who does not agree with us is not of the truth’? The important point is not whether they hear us but whether they hear God, for John assumes that what the believer says is consistent with God’s word.
Is it not presumptuous for any to say they know God? The possibility of being certain that we know God is a mystery to the world, for it has never heard his voice nor seen his shape (John 5:37). It is not presumptuous of the believer to accept the testimony of the Spirit that he is a child of God, but it is presumptuous of the world to deny that the Spirit can speak to human hearts.