Israel complained relentlessly during the wilderness wanderings, and after they complained about what they thought was their inability to conquer the Land of Canaan, the Lord said to Moses,

Then the Lord said to Moses:

“How long will these people reject Me? And how long will they not believe Me, with all the signs which I have performed among them? I will strike them with the pestilence and disinherit them, and I will make of you a nation greater and mightier than they” (Numbers 14:11–12).

They had witnessed the ten plagues upon Egypt, the crossing of the Red Sea, and the many wonderful things He had done for them on their way to the Land of Canaan, including dropping food out of the sky for them, and water from a rock, yet, they repeatedly rejected His gifts, not believing in Him, such as in this case that they could take the Land of Canaan.

Likewise, after all that Jesus did miraculously, the people killed Him, and none of the recipients of His miraculous healings showed up to defend Him.

Today, atheists want God to show Himself, but that would not do it, for they are determined to reject Him, because they do not believe Him.