1 Beloved, do not believe every spirit, but test the spirits to see whether they are from God, for  many false prophets have gone out into the world.  2-3 By this you know the Spirit of God: every spirit that confesses that Jesus Christ has come in the flesh is from God, and every spirit that does not confess Jesus is not from God. This is the spirit of the antichrist, which you heard was coming and now is in the world already. 

4 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. 5 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. 6 By this we know the Spirit of truth and the spirit of error. 7-8 Beloved, let us love one another, for love is from God, and  whoever loves has been born of God and knows God. Anyone who does not love does not know God, because God is love. 1 John 4:1-8 (English Standard Version)

In vs 4 John uses the word 'overcome'. It's a word he uses five times in this letter, twice of overcoming 'the evil one', twice of overcoming 'the world', and once, as he does here, of overcoming the spirit of the antichrist speaking through false prophets in the world. It’s a word that implies a war and a struggle. What is at stake in this war that’s taking place in the world? (vs 6)

It’s a war between truth and error. Truth here would include truth about God, about Jesus, and about real love. Error therefore would be teaching the opposite of what God is like, who Jesus was, and what real love is. Who does John say is behind the spread of deception about God and Jesus in the world? (vs 1-3)

I'm not sure of the exact meaning of those verses. Is John referring to the spirit of a man or woman, or is he referring to demonic spirits? I think it's the former, but the fact that he speaks of the 'spirit of antichrist' suggests that many false prophets are misled by demonic spirits. With regard to this war in the world the apostle Paul said: “Put on the whole armour of God, that you may be able to stand against the schemes of the devil. For we don't wrestle against flesh and blood, but against the rulers, against the authorities, against the cosmic powers over this present darkness; against the spiritual forces of evil in the heavenly places.” (Ephesians 6:11-12) What was the key issue the false prophets were attacking in John's day? (vs 2-3)

It was what we call 'the doctrine of the incarnation'. In his gospel John had written how the one who had always existed with the Father “became flesh and dwelt among us”, and how the disciples had “seen His glory, glory as of the only Son from the Father, full of grace and truth.” (John 1:14) The false prophets were denying that truth. How did John say the world in general responded to those who taught error, and those who taught truth? (vs 5)

Tragically, the world loves the lie more than the truth. Truth teaches a God who is holy, and how sin is therefore unacceptable. The lie teaches that sin is not an issue, we won't face judgement. Truth teaches that we are to love one another with the sort of love that reflects the character of God, who is love personified. The lie teaches that we are to love ourselves and use others for our own ends. We see the effects of this spiritual warfare in the news everyday. The lies are getting more brazen, sinners are more unashamed, and wickedness is promoted as the norm. God’s truth is ridiculed and rejected.

As Christians we can easily fall into despair as we see people eagerly embracing the lie and resisting the truth. But I think John had in mind the words Jesus spoke to the disciples many years earlier when He said: “I have said these things to you, that in me you may have peace. In the world you will have tribulation. But take heart; I have overcome the world.” (John 16:33) Just as Jesus triumphed over His enemies, so truth will triumph over error. There's a war on in the world – but there is a great peace in the heart of believers.