Sometimes, it is easier to live by rules. Sometimes, it's easier to have a road map of exactly how to get from point a to point b. Wouldn't it be nice to have a specific list of tasks setting out exactly how to get to heaven? Well, in the Old Testament, the Israelites were given many many rules. They failed miserably at following them. They thought they wanted the ultimate prize, but (a) I'm not sure they could all agree on what that prize was (God's favor, perhaps? or maybe wealth and a good life?), and (b) they obviously didn't want it badly enough to follow those rules.
Today's reading talks about the Old Testament rules that had been drilled into the minds of the Jews. Paul is making a distinction between the rules of the Old Testament and the new promise of the New Testament. Remember, God made a covenant with Abraham in Exodus: If Israel obeyed God fully, they would be His chosen people. Throughout the Old Testament, God gives the Israelites chance after chance to make good on this bargain. But, they still failed. As Paul says in today's reading, the whole world is a prisoner to sin.
So, God sent Jesus. Jesus is the new covenant. But, this time, instead of a set of laws and rules, God made it very simple: You can come to God through faith in Christ. Paul is quick to point out that this new covenant does not throw out the old promises made to Abraham. You still must obey God, but now, He has made it much simpler to do so - just believe that Christ died for your sins.
I find that having faith is the easy part. It's living that faith that is hard. You can ask me all day long if I believe that Christ died for my sins and that by believing in Christ I have everlasting life and I will say "Yes". But, how can I truly believe that if, after making such a declaration, I turn around and gossip about a co-worker, or drive like a maniac, or yell at my kids? We must connect our words with our hearts and that's where a road map would be nice. Sure, some of it is pretty obvious, like don't commit murder. But, typically, everyday life isn't that simple to discern.
So, when you find yourself trying to figure out if you are saying you're a Christian or if you truly are a Christian, remember today's reading. God's promise is ours if we have faith.