The one who comes from above is above all; the one who is from the earth belongs to the earth, and speaks as one from the earth. The one who comes from heaven is above all. 32 He testifies to what he has seen and heard, but no one accepts his testimony. 33 Whoever has accepted it has certified that God is truthful. (John 3:31-33)
If you think God is truthful, than you will accept and obey the words of Jesus. If you do not accept the words of Jesus you do not believe in the true God, but a different God who has been manufactured by humans.