10. Q. What is the difference between the law and the gospel?
A. The law is a doctrine that God has implanted in human nature and has repeated and renewed in His commandments. In it He holds before us, as if in a manuscript, what it is we are and are not to do, namely, obey Him perfectly both inwardly and outwardly. He also promises eternal life on the condition that I keep the law perfectly my whole life long. One the other hand, He threatens eternal damnation if I do not keep every provision of the law my whole life long but violate it in one or more of its parts. As God says in Deuteronomy 27[:26] and Galatians 3[:10], “Cursed is everyone who does not continue in all things which are written in the book of the law, to do them.” And once the law has been violated, it has no promise that by the help of the law, that is, by works of the law, our sins might be forgiven. Rather, the sentence of condemnation is imposed upon us.
The gospel of good news, however, is a doctrine of which even the wisest knew nothing by nature but which is revealed from heaven. In it God does not demand but rather offers and gives us the righteousness that the law requires. This righteousness is the perfect obedience of the suffering and death of Jesus Christ, through which all sin and damnation, made manifest by the law, is pardoned and washed away (Rom. 5; Gal. 3). Furthermore, God does not give us forgiveness of sins in the gospel on the condition that we keep the law. Rather, even though we never have kept it nor will ever be able to keep it perfectly, He still has forgiven our sins and given us eternal life as an unmerited gift through faith in Jesus Christ. John 1[:17] says, “The law was given through Moses, but grace and truth come through Jesus Christ.” And Romans 8[:3, 4]: “The law is not of faith but ‘The man who does it shall live by it.’ Christ, however, redeemed us from the curse of the law when He became a curse for us (for it is written, ‘Cursed is everyone who hangs on a tree’), that the blessing of Abraham might come upon the Gentiles in Christ Jesus and we thus might receive the promised Spirit through faith.”
Caspar Olevianus, A Firm Foundation: An Aid to Interpreting the Heidelberg Catechism, pp. 9-10