30 But, after that he had made mention of these evils, he added and said, “On account of which comes the wrath of God on the sons of unbelief.” Surely it was a wholesome alarm that believers might not think that they could be saved on account of their faith alone, even although they should live in these evils: the Apostle James with most clear speech crying out against that notion, and saying, “If any say that he have faith, and have not works, shall his faith be able to save him?” Whence also here the Teacher of the Gentiles said, that on account of these evils the wrath of God comes on the sons of unbelief.
But when he says, “Wherein ye also walked sometime, when you were living therein;” he shows sufficiently that now they were not living therein. Forsooth unto these they had died, that their life might be hidden in God with Christ. When then they were now not living in them, they were now bidden to mortify such. Forsooth, themselves not living in the same, the things were living, as I have already shown a little above, and were called their members, that is to say, those faults which dwelt in their members; by a way of speech, that which is contained through that which contains; as it is said, The whole Forum talks of it, when men talk who are in the Forum. In this very way of speech it is sung in the Psalm, “Let all the earth worship You:” that is, all men who are in the earth.
Source: On Continence (New Advent)