When Christ had told the disciples to teach others who believed the gospel what He had taught them, He had released them from any obligation whatsoever of relaying to others what Moses, the law, had once taught them.
When Christ said, “It was said long ago…But I say…”, He dismissed everything and everyone of their works as servants to make room for Himself the Son, the Faithful Servant.
Christ said to preach the gospel, the forgiveness of our sins, the good news of his resurrection. If we don’t know or remember one and the other, we will have plenty of justification to condemn our own selves and others and that’s exactly what Christ wants us to avoid because it doesn’t please God to punish us into condemnation but teach us into righteousness. His discipline is not punishment as we so often believe, but training by grace into the love and mercy that he has shown us by way of the death and resurrection of Christ. Christ suffered once for our sins and such was enough for God.
As Paul by grace had once shared to the Corinthians,
“God was reconciling the world to Himself in Christ, not counting men’s trespasses against them. And He has committed to us the message of reconciliation.” (2 Corinthians 5:19)
Preach the gospel. People won’t change in behavior unless they have hope and unless their hope is restored to God by the Word, the testimony of Jesus Christ.
Leave out the old to make room for the new.
You’re better off rejoicing in the gospel, than getting bitter over others’ behaviors or seeking joy at seeing others’ positive change in behavior.
Our joy is in what God did in Christ, not what you or anyone else could ever do.