I have a friend who believes that since God does not change, the Old Testament laws are not changed by the 2nd Covenant of Christ. What scripture(s) should I have him read?
First, it is true that scripture tells us the character of God does not change.
Jesus Christ is the same yesterday and today, yes and forever. (NASB) Hebrews 13:8
But this does not mean that God does not cause things to change. It is only His character that is unchanged. God has always been holy, and He is still holy because God cannot sin (James 1:13). God does not lie because it is impossible for God to lie (Heb. 6:18). But this does not mean God cannot make decisions over time.
Even if we assumed God could not make decisions over time, the New Covenant was a decision made before the world was created (Eph. 1:4). There was an Old Covenant which was the Mosaic Law and New Covenant which came by Jesus Christ.
. . . the mediator of a better covenant, which has been enacted on better promises. For if that first covenant had been faultless, there would have been no occasion sought for a second.
Jesus, the mediator of a new covenant, and to the sprinkled blood, which speaks better than the blood of Abel. (NASB) Hebrews 8:6-7; 12:24
Many of the Old Testament laws are still in effect because they were not replaced by Jesus’ death on the cross. May I refer you to a past Q&A dealing with the First Covenant and what parts of it apply to us today.