The moral law is eternal. We are not "bound" by it because it was fullfilled by Jesus, but it is the moral character of the God of the Bible. And because God is unchanging, his moral standards remain the same. The moral law will also be used to judge the world (including all Christ haters in this forum).You should listen to that clip where Piper talks about the 10 Commandments.
Christians are not bound by Old Testament moral law.
The moral law became pointless because of Christ.
Love Piper.