Is yonder person a condemned or uncondemned man? Ask him what he thinks of Christ. If he replies honestly, he says, “I do not accept God’s testimony about Jesus Christ; I do not receive Jesus as my Savior.” Either he claims that he does not need a Savior or else he does not feel that Jesus is the Savior he needs. He rejects the testimony of God concerning Christ. Is not that enough to condemn a man?
If a man in the very presence of the judge committed theft or murder, he would condemn himself; but is it not a still higher offense than this, in the very presence of God to do despite to his Son, by practically declaring his work and blood to have been unnecessary? Is it not the height of daring that a soul should stand in the presence of the God of mercy and hear him say in his word, “Behold the Lamb of God, which taketh away the sin of the world,” and that the soul should reply, “I have nothing to do with the Lamb of God”? What further witness do we want with regard to your enmity to God? He that will not believe in Christ would murder God if he could. His not believing in Christ is virtually to make God a liar.
From a sermon by Charles Haddon Spurgeon entitled "The Essence Of The Gospel," delivered December 4, 1870.