If it the evidence for God's existence took no effort to see and were completely un-rationalizable, then one would be insane to not follow the Judeo-Christian religion's every command, and to the T.
What would the challenge be in that?
it's very simple...
Micah 6:8 - He hath shewed thee, O man, what is good; and what doth the LORD require of thee, but to do justly, and to love mercy, and to walk humbly with thy God?
The rest of the Bible is teaching us how to do that. It's simple but nobody has done it.