This is from Mike Horton's new book The Christian Faith:
In the Reformed tradition, the law-gospel distinction was interpreted within the historical context of distinct covenants in history. The covenant of creation (also called the covenant of works or law) was based on the personal performance of all righteousness by the covenant servant. The covenant of grace is based on the fulfillment of all righteousness by our representative head and is dispensed to the covenant people through faith in him. There is still law in the covenant of grace. However, it is no longer able to condemn believers but directs them in lives of gratitude for God's mercy in Christ.
Rob Pendley