Having the understanding darkened, being alienated from the life of God through the ignorance that is in them, because of the blindness of their heart:
All Commentaries on Ephesians 4:18 Go To Ephesians 4
Clement Of Rome
AD 99
For sometimes while we are practising evil things we do not perceive it on account of the double-mindedness and unbelief that is in our breasts, and we are "darkened in our understanding"