This is what Romans 1:20 is referring to when it tells us that everything in nature is stamped with God’s signature such that no one can look at these things and not realize that there is a God. Indeed, many people have looked at nature and realized that there is a God. Some of the ancient Greek philosophers saw the handiwork of God and realized the great order and diversity inherent in nature. Many Native Americans even realized that there was a Great Spirit behind it all. Yet in spite of all this evidence, not all people will come to that conclusion.
Romans 1:21-23 explains the mindset of those that are able to look at all this greatness in nature, yet they don’t come to the same conclusion about a Creator that others of us do: “because, although they knew God, they did not glorify Him as God, nor were thankful, but became futile in their thoughts, and their foolish hearts were darkened. Professing to be wise, they became fools, and changed the glory of the incorruptible God into an image made like corruptible man—and birds and four-footed animals and creeping things.”
In spite of all this evidence, there are and always will be some who do not come to the knowledge of a Creator simply because they do not want to. 2 Peter 3:5 explains that certain people “willfully forget” or in other words are willingly ignorant of the truth, shutting their minds and understanding against any intrusion of the truth into their understanding. I’m sure you have run into such people from time to time. It seems that, no matter what you say to them, they just do not or will not admit the truth of your words of witness or the scripture or any explanation you give them. Through force of their will, they simply shut the door of their mind, not allowing any truth in, no matter what they hear. For such people, neither more explanation nor more forceful arguments will help. Only the Holy Spirit has any chance of getting through to them, leaving us with the best tool we have at our disposal in such situations, prayer to our All-Powerful God.
I pray that your understanding of God will increase every day and that you will have wisdom in any witnessing situations, being guided by the Holy Spirit in what to say and leaning on His Power through Prayer.