English Standard Version (ESV)
Think about going to the doctor. You go when you don't feel right, although you're often not sure exactly what is wrong. Once there, the doctor offers a diagnosis and then will point you toward a cure, often utilizing medicine to help nurse you back to health. The downside is that every time you get sick, you have to go back to the doctor, and each cure is only good for that particular illness.
The law serves a similar function. We know that all is not right with the world, with ourselves, with our relationships. When we slow down enough to recognize this, we go to the law and find healing for that particular ailment. The law can offer that, but it cannot cure the root cause of our sinfulness, just as a doctor cannot prevent us from getting sick again in the future. It can only fix one problem at a time. In this way, the law is a gift, because it tells us how to live and helps us order ourselves so that we are living properly, but the root problem is still present.
In Jesus Christ we have more than just a problem-solver. We have a Savior, and he has come to solve the root problem, to offer grace that does more than just cure a small ailment. In Christ, we have atonement for sin, life in place of death, mercy in place of judgment. He fulfills the law, offering the perfect sacrifice that is required for our sin so that the judgment that we deserve falls upon him.
The law cannot save us. It helps, but cannot save. Only Christ can save.