"Let the honest-hearted person compare the kind of preaching of the gospel of the Kingdom done by the religious systems of Christendom during all the centuries with that done by Jehovah's Witnesses since the end of World War 1 in 1918. They are not one and the same kind. That of Jehovah's Witnesses is really the "gospel" or "good news," as of God's heavenly kingdom that was established by the enthronement of his Son Jesus Christ at the end of the Gentile Times in 1914."
Translation; Jehovah's Witnesses preach a different gospel than that preached - and believed - by Christians in the 1st Century.
Galatians 1: 6 I marvel that YOU are being so quickly removed from the One who called YOUwith Christ’s undeserved kindness over to another sort of good news. 7 But it is not another; only there are certain ones who are causing YOU trouble and wanting to pervert the good news about the Christ. 8 However, even if we or an angel out of heaven were to declare to YOU as good news something beyond what we declared to YOU as good news, let him be accursed. 9 As we have said above, I also now say again, Whoever it is that is declaring to YOU as good news something beyond what YOU accepted, let him be accursed.