According to Christian tradition, the Law is holy, spiritual, and good, yet still imperfect. Like a tutor it shows what must be done, but does not of itself give the strength, the grace of the Spirit, to fulfill it. Because of sin, which it cannot remove, it remains a law of bondage. According to St. Paul, its special function is to denounce and disclose sin, which constitutes a "law of concupiscence" in the human heart. However, the Law remains the first stage on the way to the kingdom. It prepares and disposes the chosen people and each Christian for conversion and faith in the Savior God. It provides a teaching which endures for ever, like the Word of God.
Source: Catechism of the Catholic Church (Vatican.va)