PD writes:
Today the simple question, "Do you believe in God?" carries the question of "Do you believe he exists?" period, which is the same way we ask about things we know don't exist.
The point is, human nature by definition will deny the existance of God.
NIV writes:
Jude 17-19= But, dear friends, remember what the apostles of our Lord Jesus Christ foretold. They said to you, "In the last times there will be scoffers who will follow their own ungodly desires." These are the men who divide you, who follow mere natural instincts and do not have the Spirit.
Jesus also reminded "doubting Thomas" of the blessings that people who do not see and yet believe will have.