“Paul is basically saying that God has not kept who He is a secret. Knowing God is not hard. It’s actually the most obvious thing in the world. All you have to do is glorify Him as God and be thankful. This response, because it agrees with the truth, gives you open access to the vast treasures of the knowledge of God. But without that response, your thoughts become futile and your heart is darkened. Futile means “purposeless.” When we fail to sustain the response of thanksgiving for everything in our lives, our thinking is cut off from our purpose in God. When we lose sight of our purpose, we will inevitably make choices that are outside of God’s intentions for our lives, and this can only be destructive because it works against His design for us. A dark heart is a heart that is unable to perceive spiritual reality. It is unmoved by the desires and affections of the Lord, and therefore cannot respond to His invitation to relationship, which is the source of life. As Paul goes on to explain in Romans chapter 1, a dark heart perverts our desires and leads us into all kinds of sin that degrades our identity and relationships. The most perverted sins known to mankind came about through a door left open because of the absence of thankfulness.”