Summary: We all have ideas and ideals of how things are and how they should be that have been shaped by our experience and our world. Paul is saying we need to look away from the world to develop new values and thoughts based on God's values.
Ephesians 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. 18 They are darkened in their understanding and separated from the life of God because of the ignorance that is in them due to the hardening of their hearts. 19 Having lost all sensitivity, they have given themselves over to sensuality so as to indulge in every kind of impurity, and they are full of greed.
20 That, however, is not the way of life you learned 21 when you heard about Christ and were taught in him in accordance with the truth that is in Jesus. 22 You were taught, with regard to your former way of life, to put off your old self, which is being corrupted by its deceitful desires; 23 to be made new in the attitude of your minds;24 and to put on the new self, created to be like God in true righteousness and holiness.
What do you think about?
The wise man who wrote Proverbs said "As a man thinks in his heart, so he is" (23:7). We all have ideas and ideals of how things are and how they should be that have been shaped by our experience and our world. Paul is saying we need to look away from the world to develop new values and thoughts.
The world has multiple sources of advice on the way to live. You can turn to Google, The Wall Street Journal, Scientific American Mind, TED Talks, Cosmopolitan Magazine, The Week, the Hindu newspaper and Twitter, Snapchat, Reddit, and Facebook and find opinions about how people should live and examples of how people carry out their lives today. You can look for examples among friends, and if you don't have many of those, you can look to celebrities as your examples. All of these may be good sources of information and learning. But if these are your primary sources for determining your lifestyle, you are likely to develop a hardened heart to the LORD's way of doing things.We ALL fall prey to this.
So, Paul insists. There is another, better, and, for the Christian, necessary and mandatory way of thinking.
Put off and Put on
Have you ever seen children playing dress-up? They put on clothes, maybe of someone older. First you take off your usual clothing, then you put on something you wouldn't normally wear. Little boys might put on hats and ties-formal wear. Little girls might put on make up and jewelry they would never wear as a child. In some parts of the world even adults take this idea to an extreme around the end of October for some pagan festival-dressing like witches and vampires and superheroes and such. Paul is recommending we all play dress-up. But he's not recommending we try to look like Superman or Batman, or Wonder Woman. He's recommending we dress up like Christ.
We have to put off the old clothes-the habits, the ways of thinking, the longing for mere sensual satisfaction-and put on Christ-the love, the grace, the purity, the truth, the full commitment to the Father's will. This is both difficult and easy. The difficult part is the decision, the firm, complete decision, to say goodbye to the past of dissipation, and hello to a future of focus, to leave behind the ways our parents or friends have taught us to live and move forward to what Jesus has taught us. The decision is difficult, but changing clothes is easy. We do it every day.