What is the dividing line between the law and grace?
The dividing line between law and grace is the resurrection. Believers are on resurrection ground, not on the legal ground of the Mosaic system. Paul did not remain on Mount Sinai but carried the message of grace to the Gentiles, and the first day of the week commemorates Christ's resurrection.
Les explains that Paul spent three years in a private, personal seminary experience where the Lord revealed to him the doctrines of grace. Paul does not stay on Mount Sinai but takes the message down and out to the Gentiles, as Moses took the law to Israel. What separates law and grace is the resurrection; believers are on resurrection ground, not the legal ground of the Mosaic system. Les also notes that Paul never instructs believers to keep the Sabbath; instead, the first day of the week is significant because Christ rose from the dead. In Acts 20, after the days of unleavened bread, Paul and his companions came to Troas, and on the first day of the week the disciples came together to break bread and Paul preached. The same connotation appears in 1 Corinthians 16.