18 having their understanding darkened, being alienated from the life of God, because of the ignorance that is in them, because of the blindness of their heart;
Verses 18 and 19 demonstrate the awful futility of non-Christian orientation to life. Because of their estrangement from God, they have a dark view of life with resulting callousness toward truth.
18 having their understanding darkened,
A characteristic of pagan Gentile thinking was that their “understanding” was “darkened.” Gentiles operated from darkened understanding of God’s revelation. Bible truth did not register with them.
Ro 1: 21 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.
2 Co 4: 3 But even if our gospel is veiled, it is veiled to those who are perishing, 4 whose minds the god of this age has blinded, who do not believe, lest the light of the gospel of the glory of Christ, who is the image of God, should shine on them.
The Greek indicates that the non-Christian darkened mind is in a state of darkness (perfect tense). Their mind was darkened at some point in the past with the result that it remained in darkness. They have been blind so long that they have lost sight of the fact that they are spiritually blind.
Spiritual blindness is far worse than physical blindness (Jn 9:40, 41). These people dwelt in darkness like a fish in water—it surrounded and pervaded their existence. Non-Christians were blind to God’s truth. They were not capable to grasp divine truth or revelation.
When non-Christians turn their back to the God of light, they end in spiritual darkness.
The reason non-Christians are futile in their thinking is because they have a dark understanding of what is true. God and His Word are obscured by their negative volition.
Light biblically has to do with God’s truth. Darkness has to do with the incapacity to grapple with that truth. Darkness produces spiritual ignorance. What the lost think of as insightful is futile and without purpose. Darkened understanding and a corrupt standard of living are inseparable.