In the Bible, more a matter of wilful disobedience than intellectual doubting. The ‘fool’ who denies the existence of God (Ps. 14: 1–4) does so not by argumentation but by his perverse way of living. He refuses to seek the Lord and so has no knowledge of him. This is the major sin in the world, sin which the Spirit condemns (John 16: 9). Denial of the work of the Son of God is tantamount to making God a liar (1 John 5: 10).