The problem is not the difference between Law and Christian faith, it's faith and not works that Paul preaches. We see this in the Christian religion today; man is not perfect; no matter what sins he commits if he gives himself to Jesus he will be forgiven. It's a cop-out.
Jesus said to reach salvation you must do two things that are mentioned in the Law; love God (Deut. 6:5) and love your neighbor (Lev 19:18). That's it!
The Christian religion is divided between those that strictly adhere to Paul's faith only and to Jesus' and James faith plus works. Lot of hard line fundies believe faith alone will get you to heaven. No matter how good your works are without faith you will go to hell.
That's very different from Jesus' message.
Paul was a nasty SOB. It's from his writings that we get the hate and intolerance in the NT. It was Paul who supported slavery and the Southerns used Paul's writings to support their "peculiar institution". It's from Paul we get the hate against homosexuals. It's from Paul we get the verses that trash women, telling them to shut up in church, stay home with the kids and be submissive to the husband.
There's a big difference between Paul and Jesus. Thomas Jefferson said it best
"Paul was ... the first corrupter of the doctrines of Jesus." (Works, 1829 edition, vol. 4, p. 327.)
Some more opinions on Paul can be found here.
http://www.truthrevealed.net/paul.html
It's people like Paul that should make it evident that God did not write or inspire the Bible.