Ephesians 5:17

(5:17) "Therefore" (a conclusion is presented) "do not be foolish" (and live as unwise, "but" (a contrast is presented) "understand". "Understanding" is what you gain from application of biblical principles to your experience. It is tested knowledge that has become objective fact in your own personal life. You learn a biblical principle; you apply that in your life; you gain "understanding" as a result of seeing the principle proven in your own life and experience. It is through living-as-light that we gain a real understanding of "what the Lord's will is." This will not happen until we are living as light. Do not assume that you will know the will of God prior to any given decision. Live as light and you will understand God's will as you are going. "Having therefore gone, teach all men whatsoever I have commanded you" was the Lord's own instruction to the disciples and carries the same thought.