Our emotions are what we feel but our nature is what causes the type of reactions to the emotions, what we do concerning them. The nature of individuals is the predominant attribute which determines their essence and quality. This is why the addition of the new nature, because the old one doesn't change in that "it is enmity against God; for it is not subject to the law of God, nor indeed can be" (Rom 8:7).
The "new man" (Eph 4:24; Col 3:10) is not an entity or person, but a nature, and this is what makes us different from what we where, because it now makes us "partakers of the divine nature" (1 Pet 1:4). The new man, or nature, is what I believe the Spirit uses in our life to be "transformed into the same image from glory to glory, just as by the Spirit of the Lord" (2 Cor 3:18). The image God is transforming us into is Christ's image (Rom 8:29). The Spirit's continual application of Christ's crucifixion power to our old nature frees us live more by the new nature than by the old. We still serve sin (Rom 7:25) but not like before, as a slave under a ruler (Rom 6:12, 14).
I believe scripture teaches us that human nature is sinful. I believe since Christ's incarnation was by the Spirit, He could not inherit man's nature, as we do--from Adam. He didn't come to use what He finds but what He brings. The new nature is a creation from God (Eph 4:24; Col 3:10) and I believe that it is through this the Spirit "makes us partakers of the divine nature".