The difference between the Law of Moses as understood by the ancient Israelites in the Old Testament and the Law of Moses as taught in the Book of Mormon is fundamental. Two basic concepts of the law are not explained in a plain and precious way in the Old Testament. First, is that salvation did not come by the Law of Moses. Second, is that the purpose of the Law of Moses was to strengthen their faith in Christ. These two concepts are inextricably related but for the sake of discussion, they will be dealt with separately. Notice that of all the scriptures listed, only one comes from the Old Testament.
First, salvation does not come by the Law of Moses:
’To what purpose is the multitude of your sacrifices unto me? saith the Lord: I am full of the burnt offerings of rams, and the fat of fed beasts; and I delight not in the blood of bullocks, or of lambs, or of he goats…
Wash you, make you clean; put away the evil of your doings from before mine eyes; cease to do evil’ (Isa 1:11,16)
’For the law having a shadow of good things to come, and not the very image of the things, can never with those sacrifices which they offered year by year continually make the comers thereunto perfect…
For it is not possible that the blood of bulls and of goats should take away sins.’ (Heb 10:1,4)
’But Israel, which followed after the law of righteousness, hath not attained to the law of righteousness.
Wherefore? Because they sought it not by faith, but as it were by the works of the law. For they stumbled at that stumblingstone;’ (Rom 9:31-32)
’For the promise, that he should be the heir of the world, was not to Abraham, or to his seed, through the law, but through the righteousness of faith.’ (Rom 4:13)
’For the law made nothing perfect, but the bringing in of a better hope did; by the which we draw nigh unto God.’ (Heb 7:19)
’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.’ (Rom 3:20)
’And moreover, I say unto you, that salvation doth not come by the law alone; and were it not for the atonement, which God himself shall make for the sins and iniquities of his people, that they must unavoidably perish, notwithstanding the law of Moses.’ (Mosiah 13:28)
Second, the Law of Moses is to strengthen faith in Christ:
’…harden not your hearts, as in the provocation.
…And to whom sware he that they (the children of Israel) should not enter into his rest, but to them that believed not?
So we see that they could not enter in because of unbelief.’ (Heb 3:15-19)
’For unto us was the gospel preached, as well as unto them: but the word preached did not profit them, not being mixed with faith in them that heard it.’ (Heb 4:2)
’For Christ is the end of the law for righteousness to every one that believeth.’ (Rom 10:4)
’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.’ (Gal 3:23-24)
’Behold, my soul delighteth in proving unto my people the truth of the coming of Christ; for, for this end hath the law of Moses been given; and all things which have been given of God from the beginning of the world, unto man, are the typifying of him.’ (2 Nephi 11:4)
’And behold, this is the whole meaning of the law, every whit pointing to that great and last sacrifice; and that great and last sacrifice will be the Son of God’ (Alma 34:14)
’And for this intent we keep the law of Moses, it pointing our souls to him; and for this cause it is sanctified unto us for righteousness, even as it was accounted unto Abraham.’ (Jacob 4:5)
’For, for this end was the law given; wherefore the law hath become dead unto us, and we are made alive in Christ because of our faith; yet we keep the law because of the commandments.’ (2 Nephi 25:25)
John Taylor
“So firm a foundation having been laid for the faith of the Nephite people, we find that in every period of their history they retained their reverence for the law of Moses, though disputations sometimes arose, by reason of iniquity, with regard to its symbolism or its saving quality. The apostates, who separated themselves from the Church, occasionally fell into the grievous error of exalting the law above the Gospel, and, whilst maintaining its divine origin, they ignored its typical value and denied that it was a preparatory system leading to a higher, holier and more perfect law; they refused to recognize it as a schoolmaster to bring them to Christ.” (Mediation and Atonement, chapter 14)
See also commentary for 2 Nephi 11:4, 2 Nephi 25:25, and Mosiah 13:28-30.