Thematic Bible: Whose heart becomes darkened

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. 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].

Because when they knew and recognized Him as God, they did not honor and glorify Him as God or give Him thanks. But instead they became futile and godless in their thinking [with vain imaginings, foolish reasoning, and stupid speculations] and their senseless minds were darkened. Claiming to be wise, they became fools [professing to be smart, they made simpletons of themselves].