What is Romans ch 4, talking about. And what can we learn from it?
You don't ever give me the easy ones do you?
First of all, the main point of the body of Romans is a defense of Paul's ministry of giving the gospel to the Gentiles without them needing to become Jews first. In the first part he talks about how sinful gentiles are, and then how sinful Jews are. Then he says that the solution-- how we get connected to God-- is by faith (by committing ourselves to God's kingship through Jesus.).
The question Paul is dealing with in Romans 4 is, "So you are saying that the Law is pointless? That we never needed the Law in the first place?" Paul replies, "I'm not getting rid of the Law-- instead, I am affirming what the Law itself taught!"
So he talks about Abraham, one of the central saints in the Law, about how he was made right before God through faith, and that before he was circumcised. Thus, Paul was saying, Abraham was exactly in the same place as modern Gentiles are-- he wasn't a "Jew" in the religious sense, and he was saved by his commitment to God's kingship.
Then Paul goes on to say that this is exactly how everyone is saved, whether Jew or Gentile, and that this was the point of the Law to begin with.