1 And you were dead in the trespasses and sins 2 in which you once walked, following the course of this world, following the prince of the power of the air, the spirit that is now at work in the sons of disobedience—
Paul is talking to the Ephesians, to Christians, to you. Okay, to me too. We were dead in our shortcomings, in our sins, those things that we used to live in back when we followed the original sinner, Satan.
Notice that he says, "in which you once walked." That means that we do not walk in them any longer. It is not that we do not struggle in our flesh, but we have a means of conquering our struggles, and that is to walk in the Spirit. The alternative of not following the Spirit of God is that we are following the spirit of Satan. The spirit of selfishness.
The word "work" is the Greek word "energeo" which sounds a lot like our word "energy." So this raises the question, where do we get our energy? Those who get their energy from the Spirit of God will have the power to overcome. But those who walk in their own power, or the power of this age or of Satan will continue to struggle with their disobedience.
There is an axiom that if you don't change what you are doing, you shouldn't expect different results. If we want to see change in our lives, we need to make a more conscious effort to walk in the Spirit.