There are two things that false speakers claim: one, that they know God; and, two, they are somehow inspired to speak God’s will. The false speakers of John's day were not a hypothetical situation or a trivial side issue among the churches, but instead were very influential. The false teachers were successful enough to merit confrontation in all three of John’s letters, and are also harshly addressed by Peter, Jude and Paul.
In establishing the context of John’s warning “do not believe every spirit,” it is worth noting that the proceeding verses tell us to “believe in the name of his Son” and that this faith is confirmed “by the Spirit he gave us”:
“And this is his command: to believe in the name of his Son, Jesus Christ…We know it by the Spirit he gave us.” – First John 3:23-24
John, like Paul in 1 Thessalonians 5:19-22, does not tell believers to trust the church’s validation of spirits or to submit to denominational authority or a minister’s accreditation by ordination. John considers the individual believer responsible for judging and evaluating the genuineness of the Spirit and the orthodoxy of men who are presenting their teaching. A Christian’s love and a Christian’s trust are not to be taken for granted or given haphazardly. The object of love and trust must be tested and approved. John has already defined for the believers these contrasting values:
“Anyone who loves their brother and sister lives in the light…Do not love the world or anything in the world.” – First John 2:10 and 15
Now, he tells them:
“We know it by the Spirit he gave us. Dear friends, do not believe every spirit, but test the spirits to see whether they are from God.” – First John 3:24-4:1
The test the believer is to use is introduced by John when he says: “This is how you can recognize the Spirit of God”:
“Every spirit that acknowledges that Jesus Christ has come in the flesh is from God, but every spirit that does not acknowledge Jesus is not from God.” – First John 4:2-3
The key word in John’s test is “acknowledge.” Demons and spirits recognize the deity of Jesus, identify the humanity of Jesus and shudder because of what they know and believe to be true:
“What do you want with us, Jesus of Nazareth? Have you come to destroy us? I know who you are—the Holy One of God!” - Mark 1:24
“Whenever the impure spirits saw him, they fell down before him and cried out, ‘You are the Son of God.’ ” – Mark 3:11
“He shouted at the top of his voice, ‘What do you want with me, Jesus, Son of the Most High God? In God’s name don’t torture me!’ ” – Mark 5:7-8
“One day the evil spirit answered them, ‘Jesus I know, and Paul I know about, but who are you?’ ” - Acts 19:15
“Even the demons believe that - and shudder.” - James 2:19
The difference between the true Spirit and the false spirit, or the true man of God and the imitation pastor is the word “acknowledge,” or homologeo in the Greek which means “to say the same thing as another,” “to confess,” “to agree,” “to assent,” “to concede,” and “not to deny.” Jesus said that when the Holy Spirit came he would testify and bring glory to Jesus:
“When the Advocate comes, whom I will send to you from the Father—the Spirit of truth who goes out from the Father—he will testify about me.” - John 15:26
“When he, the Spirit of truth, comes, he will guide you into all the truth… He will glorify me because it is from me that he will receive what he will make known to you.” - John 16:13-15
“Therefore I tell you that no one who is speaking by the Spirit of God says, ‘Jesus be cursed,’ and no one can say, ‘Jesus is Lord,’ except by the Holy Spirit.” - First Corinthians 12:3
Historically, in 85 AD, John is dealing with the influence of pagan philosophies on Christian teaching. Teachings such as Gnosticism, Docetism and adoptionism that denied the fact that the eternal Son of God had come in human flesh were rising in John’s churches in Asia. All of these false doctrines taught that a mere man was chosen by God to bear his Spirit from his baptism until his crucifixion, or that the eternal Son of God did not actually become flesh but merely “seemed” (from dokeo where we get the early false doctrine of Docetism) to have flesh. But, John uses the word elelythota (“to come”) in the perfect tense right beside homologeo (“acknowledge”) to indicate that this “coming” of Christ in the flesh, or the incarnation, was a permanent change for the Son of God and that the second member of the Trinity would eternally exist in the body of the man Jesus.
Thus, John’s point was that in 85 AD the false teachers would not teach or promote what they could not accept, believe, acknowledge, or concede. The evil spirits cannot embrace the teaching that the man Jesus is the Christ who has come in the flesh to abide as a man forever. Demons and their mouth pieces (false pastors, etc.) cannot glorify that truth about Jesus Christ, but instead, they must deny it, reject it and replace it.