In Matthew 4:15-23, Jesus began his ministry with the Gospel message to repent for the Kingdom of God is at hand, which was a light to the Gentiles, and the Law of Moses was how his audience knew what sin is (Romans 3:20), so repenting from our disobedience to it is a central part of the Gospel of the Kingdom/Grace, which Paul also taught based on the Law of Moses:
Acts 14:21-22 When they had preached the gospel to that city and had made many disciples, they returned to Lystra and to Iconium and to Antioch, 22 strengthening the souls of the disciples, encouraging them to continue in the faith, and saying that through many tribulations we must enter the kingdom of God.
Acts 20:24-25 But I do not account my life of any value nor as precious to myself, if only I may finish my course and the ministry that I received from the Lord Jesus, to testify to the gospel of the grace of God. 25 And now, behold, I know that none of you among whom I have gone about proclaiming the kingdom will see my face again.
Acts 28:23 When they had appointed a day for him, they came to him at his lodging in greater numbers. From morning till evening he expounded to them, testifying to the kingdom of God and trying to convince them about Jesus both from the Law of Moses and from the Prophets.