1 Cor 1:17-18,23-24
For Christ did not send me to baptize, but to preach the gospel-not with words of human wisdom, lest the cross of Christ be emptied of its power. For the message of the cross is foolishness to those who are perishing, but to us who are being saved it is the power of God...but we preach CHRIST CRUCIFIED: a stumbling block to Jews and foolishness to Gentiles, but to those whom God has called, both Jews and Greeks, Christ the power of God and the wisdom of God.
"Let the honest-hearted person compare the kind of preaching of the gospel done by the religious systems of Christendom during all the centuries with that done by Jehovah's Witnesses since the end of World War I in 1918. They are not one and the same kind. That of Jehovah's Witnesses is really "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."
Watchtower, May 1, 1981, p. 17
But even though we, or an angel from heaven, should preach to you a gospel contrary to that which we have preached to you, let him be accursed. As we have said before, so I say again now, if any man is preaching to you a gospel contrary to that which you received, let him be accursed.