“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. 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.” (1 John 4:1-3a)
John warns his readers of the dangers of false teachers. These may come claiming to speak for Christ but they are from the spirit of the antichrist. Because of this we must reject their teaching and their “authority” because they have no real fellowship with Christ or, consequently, with us. John teaches the believer how to recognize such false brethren. They may seem to talk like a Christian and even act like one. The big test is that the true believer maintains that Jesus Christ is God incarnate. False teachers reject this in whole or in part.
The reason this is vital test of true Christian teaching is that the dual nature of Christ is at the core of our faith. Jesus had to be a real human being so He could serve as our representative and substitute to endure God’s wrath for us. He also had to be fully God so that He could offer Himself on our behalf as the sinless and perfect sacrifice. Only His death could pay the infinite price to assuage the Father’s infinite wrath.
The second test that John offers is the love of Christians for their brethren as well as all human beings. This love is the love Christ had for us, unselfish, generous, and sacrificial. This is not the love that the world admires and practices for it loves those who have not earned it or merit it. In fact the love of Christ to, in and through us is for those who not deserve it or earned it in any way. Christ Jesus loved us in this way even before we loved Him, and even though we did not deserve it. Since God is love, those who belong to Him will also love as He does.