Paul opens this section on the church’s purity just as he opened the section on unity, with an assertion claiming the authority of the Lord Jesus Christ: This I say, therefore, and testify in the Lord (4:17). His teaching in this section can be summarized in a single sentence: You cannot be the same as other people, because you are not the same as other people! The Bible is not an instruction manual on how to become a different or better person; rather it tells you that you are a different person, and be in practice what you are in fact! Simply stated, a believer is not going to look, sound, and live like the Gentiles – ignorant of God, without God in their thoughts, and void of an eternal perspective. Unlike the Gentile, the mind and life of the Christian is God-centered and eternity-focused.
There are three characteristics of Gentiles addressed in this section. First, it speaks of: the futility of their mind (4:17). It’s not that the unregenerate mind is empty, but that it is filled with vain notions. Secondly, the pagan Gentile is described as, being alienated from the life of God (4:18); that is they are insensitive to spiritual things, in the grips of spiritual death. Thirdly, they are described as, being past feeling (4:19); that is they no longer even care to hide their sin; whether through despair or wantonness, they no longer feel the reproach of their own conscience; they have lost all sense of shame. Having given themselves over to lewdness, (4:19) describes the kind of behavior that shocks public decorum with absolutely no regard for civility or the rights of others – he does not care whom he hurts, as long as he can freely express himself.