They are darkened in their understanding, alienated from the life of God because of the ignorance that is in them, due to their hardness of heart.
18. Being alienated from the life of God. The life of God may either mean what is accounted life in the sight of God, as in that passage, “they loved the praise of men more than the praise of God,” (John 12:43,) or, that life which God bestows on his elect by the Spirit of regeneration. In both cases the meaning is the same.
The apostle having gone through his exhortation to mutual love, unity, and concord, in the foregoing verses, there follows in these an exhortation to Christian purity and holiness of heart and life, and that both more general (Eph 4:17-24) and in several particular instances, Eph 4:25-32.
Commenting on Ephesians 4:17-32
Having the understanding darkened,.... Not that the natural faculty of the understanding is lost in men, nor the understanding in things natural and civil, and which is quick enough, especially in things that are evil; but in things spiritual it is very dark and ignorant, as about the nature and perfections of God, his holiness and righteousness; about sin and the consequences of it; about...