The laws of the Old Testament (or covenant) contains invaluable information and eternal insight and clarity as to those things God has approved of and disapproved of throughout history. If one carefully reads our New Testament (or covenant) doctrine, they will find that the Old Testament teachings from the law are summed up as commands given in various verses by Jesus Christ for man to now obey in faith, not a written law. In other words, we are now under a trust, to do what is right until death, at which time we then will be judged.
By the time which our Lord Jesus Christ came to establish the new covenant, the moral and spiritual lessons designed to be learned and passed from the laws given by Moses had become of little concern to the leaders of the nation of Israel whose trust the law had been committed to. To the Pharisees in particular, they had become little more than a complex legal system of some 613 laws (give or take a few) in which a mere outward profession of those laws replaced the internal meanings which were intended to be conveyed (mercy, faith, love and the like). Therefore the hypocrisy of the Pharisees had become evident and led Jesus to tell them that they were hypocrites that were willing to pay tithe of mint and anise and cummin (as the law stated they must), but they neglected the weightier matters of the law: justice and mercy and faith. Jesus concluded by telling them that though they should have still tithed, they should not have tithed without being merciful to the people and being just in cases in which justice should have been proclaimed.
The outward profession or mere show of practicing the judicial laws and ceremonial observances (tithe offerings, washing of hands, Sabbath observance etc.) had replace the heart of the commands given them by God. The leaders of Israel had become like androids without feeling nor understanding for the people and in many ways they perverted the truth, even killing the Son of God, Jesus Christ. In fact, it was so much more important to them that they appear holy, than to be holy. Jesus went on to tell them that if they had known what these words mean, 'I desire mercy, not sacrifice,' that they would not have condemned the innocent, but mercy was far from their hearts and it was evident in the way in which they treated our Lord.
As a result of not internalizing the commands of God in their own hearts, their teaching led many people astray and therefore even though Jesus came to save the nation of Israel by being a guide to them unto salvation, He came to His own, but His own did not receive Him. And as a result of the rejection by the nation of Israel of our Lord and Savior Jesus Christ and His teachings, we are told that as many as will now receive Him and put their faith in Him, to such people He has given the right to become children of God, to those who believe in His name: who are born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.
A time of change was once prophesied by the prophet Jeremiah when the Lord told him that the days are coming when He would make a new covenant, and that time has now come through Jesus Christ. Under this new covenant of grace, mandatory laws consisting of times, months, years, sacrifices and other legal observances now have no place under this new covenant. If you will thoroughly study the old testament (covenant) though, you will find that the same moral and spiritual lessons that should have been learned by Israel then, still apply to all mankind under the new coveant. Just a few of the numerous moral and spiritual lessons that the Old Testament intended to convey to the nation of Israel and now to all people are:
1. Do not think deceitfully in your heart regarding lending.
2. Do not make unjust excuses in our interactions/dealings with people, especially the poor.
3. Lend to those that may not even be able to pay you back, should they need it.
And numerous others...
In addition, we know that the underlying teachings in those laws are eternal because in the New Testament, without going into laws, and dates and times, we find our Lord Jesus Christ taught nearly the same exact messages we find taught by Moses in Deuteronomy and Leviticus. For example, the old covenant laws told the people to be kind to the poor, the new testament now tells us that when we give a feast, we should invite the poor, the maimed, the lame, the blind. And we will be blessed, because they cannot repay us; but we will be repaid at the resurrection of the just.
So as can be seen, the moral lessons attached to the laws given through Moses nearly 1,500 years before the coming of Jesus, are still reaffirmed in the New Testament scripture, and even though we do not set aside the grace of God for the law, let us also remember that the law has always taught us what God approves of. In fact, we would not have known what sin is except through the law. For example we would not have known covetousness unless the law had said, "You shall not covet." Therefore my brothers and sisters in the faith of Christ, I ask you a question:
As our beloved Paul clearly affirmed, "Do we then make void the law through faith? Certainly not! On the contrary, we establish the law." [Rom 3:31]