God's Word tells us that God has made it obvious.
Romans 1:20
20 For his invisible attributes, namely, his eternal power and divine nature,
have been clearly perceived, ever since the creation of the world,
7 in the things that have been made. So they are without excuse.
Another version:
Romans 1:18–21
18
a For the wrath of God is revealed from heaven against all ungodliness and
b unrighteousness of men, who
4 suppress the truth in unrighteousness, 19 because
c what may be known of God is 5 manifest 6in them, for dGod has shown it to them. 20 For since the creation of the world
e His invisible
attributes are clearly seen, being understood by the things that are made,
even His eternal power and
7Godhead, so that they are without excuse, 21 because,
although they knew God,
they did not glorify Him as God, nor were thankful, but
f became futile in their thoughts, and their foolish hearts were darkened.
God's Word says that to not believe is to SUPPRESS the TRUTH.