17 So this I say and solemnly testify in [the name of] the Lord [as in His presence], that you must no longer live as the heathen (the Gentiles) do in their perverseness [in the folly, vanity, and emptiness of their souls and the futility] of their minds.18 Their moral understanding is darkened and their reasoning is beclouded. [They are] alienated (estranged, self-banished) from the life of God [with no share in it; this is] because of the ignorance (the want of knowledge and perception, the willful blindness) that is deep-seated in them, due to their hardness of heart [to the insensitiveness of their moral nature].19 In their spiritual apathy they have become callous and past feeling and reckless and have abandoned themselves [a prey] to unbridled sensuality, eager and greedy to indulge in every form of impurity [that their depraved desires may suggest and demand].20 But you did not so learn Christ!
Paul in these verses discusses the ways of non-believers, and tells the Ephesians no to live as them. He mentions that the heathen live in the perverseness of their minds. They have emptiness in their souls. Their understanding is darkened, and their reasoning clouded.
They do not share a relationship with God because of ignorance which is deep inside of them. They are given to their sensuality and are eager to perform all kinds of impurity, following any thoughts that their desires guide them.