Romans 1:17 (NIV)
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."
Many popular techniques for personal evangelism begin with a question like "What do you think is required for a person to get to heaven?" or something to that effect. Many people will reply that you have to be a good person, or that you must keep the Ten Commandments. This implies that there is something in the person that merits favor from God which will earn them heaven.
To be righteous means acting in accordance with divine or moral law, to be free from guilt or sin. This verse says that the good news is that righteousness is from God. If we could supply our own righteousness then this would not be such good news, it would be redundant.
But Isaiah 64:6 says "all our righteousnesses are like filthy rags." Righteousness is not something that man can muster on his own. Go looking for it and you won't find it unless you look into the gospel. There it will be revealed and you will find that it comes from God. How can you have it? It only comes by faith. How do you live it? Again, by faith.
Thus begins the marvelous book of Romans. It is all about how a guilty man can be made righteous before a Holy God by faith.