People can be irreligious, delusional or belonging to lovers of agnosticism, ignosticism, ietsism, scepticism, pantheism, atheism, strong or positive atheism, implicit atheism, and apatheism. After the rebellion of man God saw the world turning against Him but kept hoping in a good relationship with His creatures.
In mankind's history there can be found natural theology which is generally characterized as the attempt to establish religious truths by rational argument and without reliance upon alleged revelations. Newt to it we may find lots of name-Christians trying to proof God exist but for them Jesus being God, others can see that their idea of God being Eternal, Immaterial, Transcending space, The Creator and Designer of the universe, Omnipotent, Omniscient, The unique greatest possible Being, does not fit at all their Jesus-god. Many people putting 2 and 2 together decide then wrongly because those qualities not fitting Jesus, he is not being able to be God but then there than also not being a Supreme God.