He describes this young man as simple in the bad sense of the word—he is foolish, inconsiderate, unthinking. He is "open" to all impressions of evil. He lounges near the house of ill repute, not necessarily because he plans to sin, but he does not seem all that opposed to it either! He is hanging out at a certain time and place, open to whatever might happen—no definite plans, just waiting to see how it goes. He lacks the understanding to discern the evil that is present, as well as the wisdom and courage to resist the flatteries and temptations of the seductress. In contrast, though unstated, the pure in heart—those who understand the dangers—would be at home, occupied with things that are more wholesome.
In applying this to ourselves and our efforts to forsake Babylon and steer clear of false doctrines and teachers, we can see that our individual application of verses 1-5—keeping God's commandments and making wise decisions—will help to determine whether or not we are foolish and lacking judgment. If we highly esteem God's instruction, in the letter and the spirit of the law, and if we fear God and keep His commandments, we will have the wisdom and understanding that this young man lacks.
A common saying runs, "If you fail to plan, you plan to fail." This young man may not have intended to get into trouble. He may not have planned to do anything wrong, but his approach is not aligned with I Corinthians 6:18: "Flee fornication." Paul says, "Turn around and run the other way!" The young man's approach is not one of foreseeing the dangers and avoiding them (Proverbs 22:3; 27:12), and thus he is called simple and devoid of understanding.
In the same way, if our approach is not one of striving to keep ourselves unspotted from the world, avoiding false teachers and doctrines, in essence, we are planning to fail!
David C. Grabbe
Strange Women (Part Two)