What and when God commanded, the people were to obey under threat of punishment.
Leviticus 26

Moses was the dispenser of God's commandments.
Deuteronomy 4:5-6 - Behold, I have taught you statutes and judgments, even as the LORD my God commanded me, that ye should do so in the land whither ye go to possess it. Keep therefore and do them; for this is your wisdom and your understanding in the sight of the nations, which shall hear all these statutes, and say, Surely this great nation is a wise and understanding people.

In fact, there are a number of verses that use the phrase, "the law and the prophets..."

• Matthew 7:12 - Therefore all things whatsoever ye would that men should do to you, do ye even so to them: for this is the law and the prophets.
• Luke 1:70 - As he spake by the mouth of his holy prophets, which have been since the world began:
• Luke 16:31 - And he said unto him, If they hear not Moses and the prophets, neither will they be persuaded, though one rose from the dead.

• Matthew 5:17 - Think not that I am come to destroy the law, or the prophets: I am not come to destroy, but to fulfil.
• Luke 18:31 - Then he took unto him the twelve, and said unto them, Behold, we go up to Jerusalem, and all things that are written by the prophets concerning the Son of man shall be accomplished.
• Luke 24:25-27 - Then he said unto them, O fools, and slow of heart to believe all that the prophets have spoken: Ought not Christ to have suffered these things, and to enter into his glory? And beginning at Moses and all the prophets, he expounded unto them in all the scriptures the things concerning himself.

• Numbers 15:40,41 - That ye may remember, and do all my commandments, and be holy unto your God.  I am the LORD your God, which brought you out of the land of Egypt, to be your God: I am the LORD your God.

• II Chronicles 7:17-20 - And as for thee, if thou wilt walk before me, as David thy father walked, and do according to all that I have commanded thee, and shalt observe my statutes and my judgments; Then will I stablish the throne of thy kingdom, according as I have covenanted with David thy father, saying, There shall not fail thee a man to be ruler in Israel. But if ye turn away, and forsake my statutes and my commandments, which I have set before you, and shall go and serve other gods, and worship them; Then will I pluck them up by the roots out of my land which I have given them; and this house, which I have sanctified for my name, will I cast out of my sight, and will make it to be a proverb and a byword among all nations.

How different it still is today now that we are even past Jesus' time.

It has to be 'after' the cross that it all took affect!

• Hebrews 9:16,17 - For where a testament is, there must also of necessity be the death of the testator.
• For a testament is of force after men are dead: otherwise it is of no strength at all while the testator liveth.

• See Romans 3:27,28 - Where is boasting then? It is excluded. By what law? of works? Nay: but by the law of faith. Therefore we conclude that a man is justified by faith without the deeds of the law.
• Compare that to the Old Testament who had to live by their own faith! 
• See Habakkuk 2:4 - Behold, his soul which is lifted up is not upright in him: but the just shall live by his faith.

• Romans 7:6-7 - But now we are delivered from the law, that being dead wherein we were held; that we should serve in newness of spirit, and not in the oldness of the letter. 
• What shall we say then? Is the law sin? God forbid. Nay, I had not known sin, but by the law: for I had not known lust, except the law had said, Thou shalt not covet.
• Romans 5:13 - (For until the law sin was in the world: but sin is not imputed when there is no law.
• Romans 3:30,31 - See it is one God, which shall justify the circumcision by faith, and uncircumcision through faith.
• Do we then make void the law through faith?  God forbid: yea, we establish the law.
• Romans 3:20 - Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin.
• Romans 3:21,22 - But now the righteousness of God without the law is manifested, being witnessed by the law and the prophets; 
• Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference:...

• Romans 7:25 - I thank God through Jesus Christ our Lord. So then with the mind I myself serve the law of God; but with the flesh the law of sin.

• Galatians 2:16 - Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified.
• Galatians 2:16 - Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ. 
• Romans 3:22 - Even the righteousness of God which is by faith of Jesus Christ unto all and upon all them that believe: for there is no difference:
• Galatians 2:20 - I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
• Galatians 3:22 - But the scripture hath concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe.
• Philippians 3:9 - And be found in him, not having mine own righteousness, which is of the law, but that which is through the faith of Christ, the righteousness which is of God by faith:

• Galatians 3:19-29 - Wherefore then serveth the law? It was added because of transgressions, till the seed should come to whom the promise was made; and it was ordained by angels in the hand of a mediator. Now a mediator is not a mediator of one, but God is one. Is the law then against the promises of God? God forbid: for if there had been a law given which could have given life, verily righteousness should have been by the law. But the scripture hath concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe.
• But before faith came, we were kept under the law, shut up unto the faith which should afterwards be revealed. Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith. 
• But after that faith is come, we are no longer under a schoolmaster. For ye are all the children of God by faith in Christ Jesus. For as many of you as have been baptized into Christ have put on Christ. There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus. And if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise.

• Romans 2:14-15 - For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves: Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another;)