“In this is love, not that we have loved God but that he loved us and sent his Son to be the propitiation for our sins. Beloved, if God so loved us, we also ought to love one another.” (1 John 4:10-11 ESV)
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 and sinless and perfect so that His death could pay the price of 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. He 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.