Ephesians 4:18

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:

'Being darkened in their understanding' [ tee (G3588) dianoia (G1271)]; i:e., intelligence (cf. Ephesians 5:8; Acts 26:18; 1 Thessalonians 5:4: contrast Ephesians 1:18).

Alienated - this and "darkened" imply that before the fall they (in the person of their first father) had been partakers of life and light, but had revolted from primitive revelation (cf. Ephesians 2:12).

Life of God - the life and light in Adam before the irruption of death and darkness into human nature; also the life whereby God lives in the regenerate soul Galatians 2:20). 'Spiritual life in believers is kindled from the life of God' (Bengel).

Through, [ dia (G1223) teen (G3588) agnoian (G52)] - 'on account of the ignorance;' namely, of God; Wilful ignorance originally, their fathers not 'choosing to retain God in their knowledge:' the beginning point of their misery (Acts 17:30; Romans 1:21; Romans 1:23; Romans 1:28; 1 Peter 1:14).

That is in them - deep-seated, indwelling: the defect of the intellect, owing to the defect of the heart.

Because of - on account of.

Blindness, [ pooroosin (G4457), from pooroo (G4456)] - from pooros (a kind of stone): to petrify; to make hard; literally, used of the skin, so as not to feel the touch. Hence, a soul's callousness feeling (Mark 3:5). Where there is spiritual "life," there is feeling; where there is not, there is 'hardness.'