As I understand it: covenants cannot be modified. They are made and binding, and extinguished if they are broken. Gods word is everlasting however, so his laws existed before they were written in stone, and stand to this day. The book of the law (witness against Israel) was put in place temporarily until messiah came, as stated in (Gen 49:10) “The scepter shall not depart from Judah, Nor the ruler's staff from between his feet, Until Shiloh comes, And to him shall be the obedience of the peoples.” A quick study of the Hebrew words reveals that scepter also means affliction; so the affliction of the Jews will remain until Jesus comes. There isn’t necessarily a single book that goes into all the distinctions, but when you understand them, all of Paul’s letters are in perfect harmony with the law. I wish it was clearly laid out to avoid all the confusion, but I think God set it apart for the Holy Spirit to reveal through study by the true seekers of understanding. Unfortunately most churches don’t understand and toss the law and commandments out with the book of the law, so the entire Old Testament no longer applies in their opinion. Most Christians seem to think that “Old Testament God” and Jesus are not one and the same. He is teaching the same laws and commandments, from the beginning until the end. The gospels, among many things, tell a story about the apostles not recognizing the purpose Jesus came to earth. They thought he was there to establish his kingdom and rule as king, while they’d have high ranking positions. It wasn’t until after his death and resurrection that they realized his business here was to tie up loose ends from the past sins committed, clarify the laws and commandments (as they were being corrupted by the priests and temple, doctrines of men being passed off as commandments of God), and to establish his covenant with a new people, true Israel, who were scattered throughout all nations unbeknownst to them (us). He is the Passover lamb, his death is the feast of unleavened bread, his resurrection is the feast of first fruits etc. All that is written in the OT is absolutely relevant to us today, and even the writings throughout the book of the law do a great job of adding details about God’s laws and feasts. We study the old events as historical, understanding how it happened again semi-metaphorically during Jesus’ life, and look for them to happen a third time to be ready upon his return.