The second function of the law and its works-principle was to show Israel's inability to meet the moral requirement of the law on its own, thus showing its need of a Savior. The demand of the law easily exposed Israel's moral failure and inability. But was that enough to make them see their need of a Savior--not just a Savior to defeat their enemies and establish a kingdom of prosperity and peace but also a Savior to deliver them from their sin? This was not as instinctive and automatic as we might think because the Mosaic Covenant--in fact, the law itself--had the sacrificial system built into it.
The presence of this sacrificial system pointed to the gracious nature of the Mosaic Covenant. A covenant of works cannot have any provision for forgiveness: one strike and you are out, as it was with Adam and Eve in the Garden of Eden. But how would Israel come to see the inadequacy of the sacrificial system to deal with their problem of sin and thus their need of a Savior? Why would they worry about their sins as long as the temple was standing and the sacrifices were being offered on the altar, just as God commanded precisely for the forgiveness of their sins?