When it comes to Christianity there are many lies and falsehoods spread around. Sadly many are even believed by the believers. This thread will tackle a couple of these issues, and maybe one of the most important ones, namely the relation and importance of the Old Testament to the New Testament, as well as the relationship of judaism to Christianity.
To adress the later we first need to make clear what the Chrstian stance is/should be to the teachings of the old prophets.

To make it short, its all correct and accurate. Beyond being historic accounts and lessons laught through those, it also are records of God building a relationship with humanity, and teaching us the basic things He desires of us. Christ Himself makes constantly quotes and refers to the old scriptures to make His points. He also says clearly
>46 If you had believed Moses, you would believe Me, because he wrote about Me. 47But since you do not believe what he wrote, how will you believe what I say?”
And the correctness of the law He also directly affirms
>17Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them, but to fulfill them. 18For I tell you truly, until heaven and earth pass away, not a single jot, not a stroke of a pen, will disappear from the Law until everything is accomplished

So what does Paul then mean when he tells us
>14For sin shall not be your master, because you are not under law, but under grace.
and
>8For it is by grace you have been saved through faith, and this not from yourselves; it is the gift of God, 9not by works, so that no one can boast.
He means that works can not justify us. The only thing our works earn us is death through our sins.
>23For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
If the salvation were earned it would no longer be a gift, and as such
>4Now the wages of the worker are not credited as a gift, but as an obligation.