".... in Ephesians 4:17–19, which the author exegeted. Verse 18 must be referring to people like atheists,
“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.”
...“the root of the problem, apparently, is not a lack
of intelligence but rather a hardness of heart that is itself caused by immoral
behavior”.
For out of the heart proceed evil thoughts, murders, adulteries, fornications, thefts, false witness, blasphemies: Matthew 15:19 states that immoral behavior proceeds from
the heart.
So there seems to be a progression whereby evil hearts
---give birth to
evil thoughts
---which become evil deeds.
---Then evil hearts become hardened.
This destructive process cripples intellect,
or darkens understanding."
ICR