Sorry, I reject this interpretation of St. Paul's words--that the Old Testament was primarily a device by God to foreshow that the Law was impossible to keep. This is a novel emphasis that only came about with the emergence of Protestantism. The Old Testament is much more than that: it shows (among many other things) the eternal character of God and how he deals with his people and how, while most of his people simply did not even try to keep the Law, there were some exceptions (such as I cited) and others (whose faith is lauded in the Book of Hebrews; etc.). Really, if one is a true student of the WHOLE Bible, it's major recurring and connecting theme is not Moses and the Law (Moses is barely mentioned in the OT after the Pentateuch), but about David and his kingdom that is going to be fulfilled by Jesus and the Kingdom of God.
This is a major biblical interpretive difference between Catholics and Protestants (and, yes, I've studied it from both perspectives in 30+ years of Bible study) and we're not going to resolve it here.
How typical - reject that which doesn’t fit your wished for perception and then cite others as your proofs...how convenient....because your “religion” tells you to ignore the parts that weaken those who control your religion....