Does the old nature war against the new nature in a Christian?
Yes. The old nature declares war on the new nature, and the new nature must war against the old, producing constant battle from salvation until death or Rapture. These two forces within every believer are contrary, at total odds, and war constantly.
Les explains that the old nature declares war on the new nature, and consequently the new nature has to declare war on the old nature, so it is a constant battle. The battle lines are defined from the moment we are saved until we leave this life, either by death or the Rapture; until then believers are in constant warfare. The old Adam, the flesh, lusts or wars against the Spirit, and the Holy Spirit wars against the flesh or old Adam. These two forces within each and every believer are contrary and at total odds; they cannot agree on anything. The new nature has a whole new set of values in compliance with the righteousness, holiness, and laws of God, whereas the old nature, whose god is Satan and the god of this world, is bent in rebellion and unbelief. Thus they are two totally opposites and war constantly, so you cannot do the things you would.