John Piper once preached:
What Then Shall Those Who Are Justified Do with the Law of Moses?
Read it and meditate on it as those who are dead to it as the ground of your justification and the power of your sanctification. Read it and meditate on it as those for whom Christ is your righteousness and Christ is your sanctification. Which means read and mediate on it to know Christ better and to treasure him more. Christ and the Father are one (John 10:30; 14:9). So to know the God of the Old Testament is to know Christ. The more you see his glory and treasure his worth, the more you will be changed into his likeness (2 Corinthians 3:17-18), and love the way he loved – which is the fulfilling of the law (Romans 13:10).
I say it again. What shall you do with the law – you who are justified by faith alone apart from works of the law? Read it and meditate on it to know more deeply than you have ever known, the justice and mercy of God in Christ, your righteousness and your life.