How does old Adam react when you see something your neighbor owns?
Old Adam reacts with covetousness, envy, and greed. When a person sees that a neighbor owns something, old Adam immediately says, 'I've got to have that because my neighbor's got it.' This is the sinful production center Paul warns against, and believers are not to live on that plain.
Les explains that old Adam never quits working on us and is the part of us that becomes greedy, envious, and covetous. So when you see something your neighbor has, the first thing old Adam says is, 'Hey, I've got to have that because my neighbor's got it.' Paul warns against living that way, because believers no longer live on that plain. The deeper problem, as Les points out, is not merely sinful acts but the production center of those thoughts and sins, which is old Adam.