1 John 4:6

We are of God
Not only as the chosen of God, the children of God, regenerated ones, and believers, but as ministers of the Gospel; they were chosen, and called, and sent of God to preach the Gospel, and were qualified for it, by gifts received from him, and had their doctrine from him, as well as their commission and mission: they were not of the world, and therefore did not speak of the world, nor things suited to worldly men; but being of God, they spoke the words of God, which were agreeable to him, which made for the glory of the three divine Persons, and were consistent with the divine perfections; which maintained the honour and dignity of the persons in the Godhead; which magnified the grace of God in salvation, and debased the creature:

he that knoweth God;
not only as the God of nature and providence, but as in Christ, and that not only professionally, but practically; that has an experimental knowledge of him, that knows him as exercising lovingkindness, having tasted of his grace and goodness; that knows him so as to trust in him, and love him; for such a knowledge of God is meant, as has true real affection to him joined with it; so that it is he that loves his name, his glory, his truths, and his ordinances: he

heareth us:
not only externally, constantly attending on the ministry of the word, as such do; but internally, understanding what is heard, receiving it in love, cordially embracing it, and firmly believing it, and acting according to it:

he that is not of God;
who is not born of God, but is as he was when born into the world, and is of it: and who does not righteousness, nor loves his brother, nor confesses the divinity, humanity, and offices of Christ, and so is not on the side of truth, nor has the truth of grace in him; see ( 1 John 3:10 ) ( 4:3 ) ; such a man

heareth not us;
he is a mere natural man, a carnal and unregenerate man; and such an one cannot attend on a Gospel ministry, or receive Gospel doctrines, which are with him senseless, stupid, and foolish notions, yea, foolishness itself; nor can he know and understand them through ignorance, and want, of a spiritual discerning; they are hard sayings, and he cannot hear, nor bear them; and when this is the case, it is a plain token of unregeneracy, and that such persons are not of God; see ( John 8:47 ) .

Hereby know we the spirit of truth, and the spirit of error;
the difference between truth and error; can distinguish one from another, and discern who are the true ministers of Christ, and who are the false teachers; for not only the word of God, the Scriptures of truth, are the test and standard, the touchstone to bring them to, and try them by; and the doctrines they severally bring show who they are; but even their very hearers distinguish them. Spirits, or men pretending to the Spirit of God, may be known in a great measure by their followers; they who have the spirit of error, and are of the world, they are followed, and caressed, and applauded by the men of the world, by unregenerate persons; they who have the spirit of truth, and are of God, they are heard and approved of, and embraced by spiritual men, by such who know God in Christ, and have tasted that the Lord is gracious.