Why do believers still struggle with sin after salvation?
Believers still struggle because the flesh, old Adam, wars against the indwelling Spirit, and the Spirit wars against old Adam. This internal conflict continues after salvation, so walking in the Spirit is necessary to avoid giving in to the old desires of old Adam.
Les explains that the conflict proves the point: the flesh, or old Adam, lusts or wars against the Spirit, and the indwelling Spirit wars against old Adam. He illustrates this with the anecdote of a man saved out of degradation and alcoholism who had to pass his old bar daily. He described two little dogs inside fighting—a black dog saying to go back to the old lifestyle and a white dog saying to go get the mail. Asked which wins, he said, the one I feed the best. Les teaches that believers must walk in the Spirit, that position of being in Christ, and then they will not give in to the old desires of old Adam.