What does Ephesians 4:18 mean?

Paul uses the concept of Gentiles in this passage as a reference to those who are apart from the family of God. In other words, in this instance, Paul is referring to unbelievers. Such people are given two characteristics in this verse. First, their ability to understand what is right is blocked from the "light" of God. Believers, on the other hand, are to love the Lord with "all the understanding" (Mark 12:33). Paul notes elsewhere that false teachers lack understanding (1 Timothy 1:7); it is the Lord who gives understanding (2 Timothy 2:7; James 3:13).

Second, unbelievers are separated from God, and the life He gives in salvation. An unbeliever cannot experience God in his or her life apart from salvation by grace through faith (Ephesians 2:8).

Paul also provides two reasons explaining why these characteristics are true. First is not knowing or understanding God's ways. This "ignorance" has nothing to do with intelligence, as the second point demonstrates. This subsequent detail is that unbelief is not fundamentally mental, but moral. An unbeliever lives a life with a heart hardened against God, so they cannot understand what God tries to teach them (John 7:17; 1 Corinthians 2:14).