"Now this I say and testify in the Lord, that you must no longer walk as the Gentiles do, in the futility of their minds. They are darkened in their understanding, alienated from the life of God because of the ignorance that is in them, due to their hardness of heart." (Ephesians 4:17-18 ESV)
"Now go through the whole of your Bible and you will find that this is what it says everywhere about man in sin and about man outside Christ. It describes the kind of life people live, and then it asks its question, Why do they live like that? There is, says the Bible, only one explanation: the failure is in their minds, their intellects, and their understanding. The highest faculty in man has become blunted and blinded; he cannot see because of this pall that has descended upon him; he is surrounded by darkness. But let me put this a little more theologically. The most disastrous effect that the Fall of Man produced upon man was in his understanding. That is the whole of the biblical explanation of why man is as he is and why the world is as it is. God created man perfect, endowed him with amazing faculties, made him lord of creation and of the universe; and yet we see something so entirely different. Why the difference? What has happened is that man sinned, he disobeyed God, and he fell. And the Fall has had the most disastrous consequences upon man and upon his whole life and living; and of all its terrible effects the most disastrous and devastating is upon the mind of man. It has darkened his understanding."
~ Martyn Lloyd-Jones, Darkness and Light: An Exposition of Ephesians 4:17--5:17 (Baker Books, 1982), p. 42.