Why does Paul say he is brought into captivity in Romans 7?
Paul says he is brought into captivity because another law in his members wars against the law of his mind, making him captive to the fact of life that old Adam is in his members. This old Adam is under Satan's control, so the new nature and old nature are in continual warfare.
Les explains that Paul is describing a fact of life: since conversion, Christ dwells within the believer by the Holy Spirit as the inward man. But Paul sees another law warring against the law of his mind, bringing him into captivity to the fact of life that old Adam is in his members. This is a warfare between the new nature and the old, and old Adam is under Satan's control. Les notes Paul has not yet mentioned the Holy Spirit's power in these first seven chapters; that breaks out in chapter 8, where Paul asks who shall deliver him from the body of this death and old Adam's influence.
But I see another law in my members, warring against the law of my mind, and bringing me into captivity to the law of sin which is in my members.