One of the best treatments of the law of God can be found in the Westminster Larger Catechism. I can't highly recommend enough to take time to read through it and pay careful attention to the Scripture proofs. Here is an online copy:
Westminster Larger Catechism 91-150
Below is a couple excerpts showing that the moral law was given to Adam and also that it is useful for the regenerate man. We could go in circles but I hope on any discussion I would give would be to merely restate what is already stated there - and I would probably goof it up. More than likely Mr. Winzer, Jacob or most others will be doing the same.
Q. 92. What did God at first reveal unto man as the rule of his obedience?
A. The rule of obedience revealed to Adam in the estate of innocence, and to all mankind in him, besides a special command not to eat of the fruit of the tree knowledge of good and evil,
was the moral law.
[398]
[398] Genesis 1:26-27. And God said, Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth. So God created man in his own image, in the image of God created he him; male and female created he them.
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 show 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
Romans 10:5. For Moses describeth the righteousness which is of the law, That the man which doeth those things shall live by them.
Genesis 2:17. But of the tree of the knowledge of good and evil, thou shalt not eat of it: for in the day that thou eatest thereof thou shalt surely die.
Q. 93. What is the moral law?
A. The moral law is the declaration of the will of God to mankind, directing and binding every one to personal, perfect, and perpetual conformity and obedience thereunto, in the frame and disposition of the whole man, soul and body,
[399] and in performance of all those duties of holiness and righteousness which he oweth to God and man:
[400] promising life upon the fulfilling, and threatening death upon the breach of it.
[401]
Q. 94. Is there any use of the moral law to man since the fall? (presupposes its existence prior to the fall...)
A. Although no man, since the fall, can attain to righteousness and life by the moral law:
[402] yet there is great use thereof, as well common to all men, as peculiar either to the unregenerate, or the regenerate.
[403]
Q. 97. What special use is there of the moral law to the regenerate?
A. Although they that are regenerate, and believe in Christ, be delivered from the moral law as a covenant of works,
[414] so as thereby they are neither justified
[415] nor condemned;
[416] yet, besides the general uses thereof common to them with all men, it is of special use, to show them how much they are bound to Christ for his fulfilling it, and enduring the curse thereof in their stead, and for their good;
[417] and thereby to provoke them to more thankfulness,
[418] and to express the same in their greater care to conform themselves thereunto as the rule of their obedience.
[419]
[414] Romans 6:14. For sin shall not have dominion over you: for ye are not under the law, but under grace.
Romans 7:4, 6. Wherefore, my brethren, ye also are become dead to the law by the body of Christ; that ye should be married to another, even to him who is raised from the dead, that we should bring forth fruit unto God.... 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.
Galatians 4:4-5. But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law, To redeem them that were under the law, that we might receive the adoption of sons.
[415] 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.
[416] Galatians 5:23. Meekness, temperance: against such there is no law.
Romans 8:1. There is therefore now no condemnation to them which are in Christ Jesus, who walk not after the flesh, but after the Spirit.
[417] Romans 7:24-25. O wretched man that I am! who shall deliver me from the body of this death? 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 3:13-14. Christ hath redeemed us from the curse of the law, being made a curse for us: for it is written, Cursed is every one that hangeth on a tree: That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith.
Romans 8:3-4. For what the law could not do, in that it was weak through the flesh, God sending his own Son in the likeness of sinful flesh, and for sin, condemned sin in the flesh: That the righteousness of the law might be fulfilled in us, who walk not after the flesh, but after the Spirit.
[418] Luke 1:68-69, 74-75. Blessed be the Lord God of Israel; for he hath visited and redeemed his people, And hath raised up an horn of salvation for us in the house of his servant David.... That he would grant unto us, that we being delivered out of the hand of our enemies might serve him without fear, In holiness and righteousness before him, all the days of our life.
Colossians 1:12-14. Giving thanks unto the Father, which hath made us meet to be partakers of the inheritance of the saints in light: Who hath delivered us from the power of darkness, and hath translated us into the kingdom of his dear Son: In whom we have redemption through his blood, even the forgiveness of sins.
[419] Romans 7:22. For I delight in the law of God after the inward man.
Romans 12:2. And be not conformed to this world: but be ye transformed by the renewing of your mind, that ye may prove what is that good, and acceptable, and perfect, will of God.
Titus 2:11-14. For the grace of God that bringeth salvation hath appeared to all men, Teaching us that, denying ungodliness and worldly lusts, we should live soberly, righteously, and godly, in this present world; Looking for that blessed hope, and the glorious appearing of the great God and our Saviour Jesus Christ; Who gave himself for us, that he might redeem us from all iniquity, and purify unto himself a peculiar people, zealous of good works.