Eph 4:17 So I tell you this, and insist on it in the Lord, that you must no longer live as the Gentiles do, in the futility of their thinking.   

   

  

This is Paul in full instructional mode! He's not only telling them something, he insists they do this. This is not a matter for negotiation or debate, you need to do this! So what is the ‘this'? It is a negative, to stop living like the Gentiles. Hold on, most of us today are Gentiles, non-Jews. Yes, but the sense he uses means the ungodly world majority who refuse to follow God. Their thinking, he says, is futile.

 

You've heard the catch phrase from Star Trek: “Resistance is futile!” It means hopeless and pointless. The thinking of the godless world is hopeless and pointless. In what follows he talks about that world being separated from God, ignorant of Him because they've hardened their hearts against Him, they are insensitive to spiritual things and focus purely on sensual things and impurity. You are NOT to live like that now, he says to the Christians at Ephesus and to us.

 

In the verses before he speaks about being blown all over the place by different ideas that lead astray. That is what happens when there is godless thinking, you get pushed all over the place by competing ideas. No, says Paul, that's not for you any more. We're to be established in Christ, in his word with lives of understanding, experiencing the Lord, sensitive to spiritual matters, completely pure and holy. That is his call to us.