I am not ashamed of the gospel, because it is the power of God for the salvation of everyone who believes: first for the Jew, then for the Gentile. For in the gospel a righteousness from God is revealed, a righteousness that is by faith from first to last, just as it is written: "The righteous will live by faith."
Romans 1:16-17 (NIV)
What is "the gospel?"
The word "Gospel" means "Good News." A gospel presents the Good News that Jesus Christ has made salvation available to all people, not just Jews.
As Paul makes clear, there is only one gospel:
Now, brothers, I want to remind you of the gospel I preached to you, which you received and on which you have taken your stand. By this gospel you are saved, if you hold firmly to the word I preached to you. Otherwise, you have believed in vain.
For what I received I passed on to you as of first importance: that Christ died for our sins according to the Scriptures, that he was buried, that he was raised on the third day according to the Scriptures, and that he appeared to Peter, and then to the Twelve. After that, he appeared to more than five hundred of the brothers at the same time, most of whom are still living, though some have fallen asleep. Then he appeared to James, then to all the apostles, and last of all he appeared to me also, as to one abnormally born. Whether, then, it was I or they, this is what we preach, and this is what you believed.
1 Corinthians 15:1-8,11 (NIV)
Is there a penalty for distorting the gospel?
Jesus, voluntarily, underwent a horrible, torturous, humiliating death for our sake! He wants to be remembered and honored for His loving sacrifice, and justly so.
Through Paul He has warned that He will not ignore those who teach a different gospel and that He will punish those who distort the truth:
I am astonished that you are so quickly deserting the one who called you by the grace of Christ and are turning to a different gospel -- which is really no gospel at all. Evidently some people are throwing you into confusion and are trying to pervert the gospel of Christ. But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let him be eternally condemned! As we have already said, so now I say again: If anybody is preaching to you a gospel other than what you accepted, let him be eternally condemned!
Galatians 1:6-9 (NIV)
Then Jesus spoke to them again, saying, "I am the light of the world. He who follows Me shall not walk in darkness, but have the light of life."
John 8:12