The glorious Gospel of Jesus Christ sets us free from living under guilt and condemnation. Jesus Christ died and paid the price for our sins, in order for us to be set free and live victorious lives. The Old Testament (before Jesus came) shows that people had to follow the ten commandments. These were given for people to understand their sinful condition. The New Testament (when Jesus came) shares the good news: Righteousness with God can only be achieved through faith in Jesus Christ (it is not our own doing by keeping the ten commandments). No matter how hard we try, we can NOT obey all of God's commandments.
The only one without sin is Jesus Christ. The good news is that by putting our trust in Jesus Christ (who knew no sin, but become sin for us), we become blameless and righteous in God's sight. This salvation is the free gift of God to us, the sinners: It is by grace that we are saved not by our own efforts (good works).
We can't leave both under the law (the old covenant) and under God's grace (the new covenant). The Bible tells us that no one can keep the law (the old covenant), and that all who rely on the law are under a curse: "Cursed is everyone who does not continue to do everything written in the Book of the Law." (Galatians 3:10)
Living under grace is what God wants for us. In the book of Galatians, apostle Paul addresses this issue. He asks Galatians who has bewitched them. These are Christians Paul is talking to. They have been saved by hearing the Gospel (the good news), and received the Spirit of God because they believed in Christ Jesus. "You foolish Galatians! Who has bewitched you? Before your very eyes Jesus Christ was clearly portrayed as crucified. I would like to learn just one thing from you: Did you receive the Spirit by the works of the law, or by believing what you heard? Are you so foolish? After beginning by means of the Spirit, are you now trying to finish by means of the flesh? (Galatians 3:1-3)
The problem that Galatians faced, as many Christians today, is that somehow they departed from the reality of the cross. They started through faith in Jesus Christ but after that they tried to achieve righteousness with God through their own efforts.
God says that "our acts of righteousness are like filthy rags" (Isaiah 64:6), and that "no one is justified before Him by the law" (Galatians 3:11). On the contrary, God wants us to live by faith: "The righteous will live by faith" (Galatians 3:11)