In Luke's Gospel Jesus tells an expert in the law to do what the law says if he wants to inherit eternal life (Luke 10:25). But in Acts Peter declares, "through the grace of the Lord Jesus we believe to be saved" (Acts 15:11). Explaining the relationship between these two apparently conflicting statements about works and faith is only one of the puzzles that make grasping what Luke says about the law so challenging.
In any case, reducing the Christian value of the law to a via media or to a concern for its sociological effects (e.g., to legitimate Christianity in Roman eyes by linking it to ancient Jewish tradition), seems to underplay its continued significance for Acts. It is as if "salvation" is such a big thing, that we can't appreciate any subsidiary and on-going role for the law.
(For earlier thoughts on salvation in Luke-Acts see this post, and follow the links back.)
Photo credits: Big Four Ice Caves, Washington (more links here and here). Don't worry, we didn't go inside.