1 John 4:4-6 say….
Little children, you are from God and have overcome them, for he who is in you is greater than he who is in the world. They are from the world; therefore they speak from the world, and the world listens to them. We are from God. Whoever knows God listens to us; whoever is not from God does not listen to us. By this we know the Spirit of truth and the spirit of error.
The false prophets that John has been warning about are “from the world” rather from God. Consequently their message is from the world and their willing audience is the world.
John’s “dear friends” (v1) however are from God. What John does here is set a clear distinguishing line between those who are from the world and those who are from God.
It strikes me that you can break down verses 5-6 like this:
1) They are from the world
1,i) Therefore they speak from the world
1,i,i) The world listens to them
2) We are from God
2,i) Implied by the context but not explicit.. therefore our message is from God
2,i,i) Whoever knows God listens to us
2,i,i,i) And… Whoever is not from God does not listen to us.
3) This is how we know the Spirit of truth and the spirit of error.
How can I tell if I am from God or from the world? I should ask myself whose message I listen to. Which is more attractive to me? If I am an avid hearer of the world’s message, eager for novelty and ideas that are utterly inconsistent with the gospel, I should be warned that I lack evidence that I am from God. If on the other hand I am eager for the message of truth, God’s message, the apostle’s teaching, the Biblical gospel, then I should be reassured that I know God.
To put all this in another way, one of the authenticating marks of the work of the Holy Spirit is a readiness to listen to God’s message.