"For I know that in me (that is, in my flesh,) dwelleth no good thing: for to will is present with me; but how to perform that which is good I find not. For the good that I would I do not: but the evil which I would not, that I do." (Romans 7:18-19)
Excited, expedited
In other words, Paul's a changed man. Overnight, it would seem, he has acquired this new desire to live from a new center. Re-word it how you will, what you get upon believing in Jesus is at once life changing, world altering and all-around-mind-blowing. And I'm not even getting into the mechanics of it. You have met your Creator—now your "Father which is in Heaven" (Matthew 5:45). Do you actually believe this stuff? Actually, yes. But this is just the beginning. Paul expresses above, the acknowledgment of his powerlessness in the face of God's (still) exacting standards. You thought it was smooth sailing and cheap grace and lots and lots of lounging around doing nothing. Basking in the orange glow of the stained-glass windows as you make your way from this life to the next. I'm telling you, now you've acquired the pilot light of your salvation, all the dark you heretofore thought was light will be seen for what it is. An active, living black that seeks to keep you under. The key against this stuff, is when Paul says "for to will is present with me". We now have, as Peter says "a lively hope by the resurrection of Jesus Christ from the dead." (1 Peter 1:3)
"And if Christ be in you, the body is dead because of sin; but the Spirit is life because of righteousness." (Romans 8:10)
Worth its saltation
"And Paul said, I would to God, that not only thou, but also all that hear me this day, were both almost, and altogether such as I am, except these bonds." (Acts 26:29, emphasis mine)
Along with the re-creation of our spirit into something new, comes this desire to please God. Paul's letter to the Christians in Rome is so dense, it's ridiculous. Years of life and suffering and reorientation in our thinking to be more in line with Christ (whatever it takes, and you should totes check it out) is but part of what's required to wrap our minds around the clear exposition of Paul. Brilliant. To will is present with me. Take heart. Many Christians, myself included, worry and wonder about their salvation in spite of this simple, substrate and undergirding fact: you wouldn't even care nor have the desire to please God were you not a child of His. But we're still here in this house. Carrying around our "baby spirit", for lack of a better term, is this body. "These bonds" as Paul no doubt took the idea one further, being imprisoned for the Gospel, stretching forth his shackled wrists in the presence of King Agrippa. What Paul went through up to martyrdom, even as Christ did before him, we get to experience in light—the aforementioned pilot light—of a body that struggles with what it does.
"From whence come wars and fightings among you? come they not hence even of your lusts that war in your members? Ye lust, and have not: ye kill, and desire to have, and cannot obtain: ye fight and war, yet ye have not, because ye ask not." (James 4:1-2)
In Evolutionary Theory, the term "hopeful monsters" refers to slight and subtle changes within a small group and leading out to larger, thus affecting species as a whole. And while my one-sentence paraphrase is probably, uh, wrong, I will say that the spiritual change upon believing in Jesus is instant. Heck, you may even have to deal with some generational issues from progenitors gone by, but the change has happened. You are not who you once were upon birth and you may not even be who your parents thought (!). All of this tells to the once-and-for-all gift of salvation through Jesus Christ.
The body? God knows.