Romans 3:20

Romans 3:20
When my 4yr old brings me a paper she's written on, she thinks she's doing REALLY well. She is...for a 4yr old. But her letters aren't consistent, they're not yet well-proportioned, they can be difficult to decipher, and they only spell actual words when she has asked for a lot of help. Her "words" look good to her only because she doesn't know any better yet.
The Law shows us just how far we are from the perfect righteousness of God. We may be doing really well for a mere fallen human, but our efforts are not consistent and fall short in many, many ways. Most of us probably don't even realize how limited our successes are. We bring our results to God for Him to admire us without comprehending how hard it is to even recognize them as righteousness. Reading the Law and attempting to fulfill it teaches us what perfect righteousness looks like. It reveals all the mistakes and sins we make without even recognizing them as sins. It teaches us what the real thing is so we can learn to see the innumerable ways we still need to improve.