Romans 1:20 For the invisible things of him from the creation of the world are clearly seen, being understood by the things that are made, even his eternal power and Godhead; so that they are without excuse: 21 Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.
There is no excuse when Christ returns as all will have heard the Gospel preached to them, but yet many reject for they lack understanding as they would rather be lovers of self. If they only knew what they will be missing. Hosea 4:6, 7