But now I (new nature), on my part, no longer work it out for myself, but the dwelling in me sin [nature] (Romans 7:17).
When we work out the things we do not desire to do—the works of the flesh—it is not the new nature we have in Christ that is producing them. By applying law, our intent is to bring about what is good; yet in the end, we work out the very things we do not desire to do.
Since it is the sin nature that dwells in me which works out the things I do not desire to do, I must apply the truth—the doctrine for overcoming the sin nature—in order to work out the righteous things my new nature desires. This cannot be accomplished through law, for, as Paul has already clearly demonstrated, the sin nature uses the law to deceive and thereby works out the very things we do not desire to do.