The main theme of the Bible is that people should obey LORD - keep his Laws and Commandments. Those who break the Law will be cursed, and those who keep the Law will be blessed.
But people cannot do it on their own - they lack the proper "software". Once he believes in Jesus - LORD GOD will give him this piece of "software" to do right. And then he is able to fulfil the Laws and Commandments. This piece of software is not given on the condition of works, i.e. how many hours of social work, how many days of fasting, how much good works done, .... It is entirely a free gift, hence we called it "grace of LORD".
But does it mean the old Laws and Commandments are abolished ? NEVER. Jesus : Think not that I have come to abolish the law and the prophets; I have come not to abolish them but to fulfil them. For truly, I say to you, till heaven and earth pass away, not an iota, not a dot, will pass from the law until all is accomplished. Whoever then relaxes one of the least of these commandments and teaches men so, shall be called least in the kingdom of heaven; but he who does them and teaches them shall be called great in the kingdom of heaven. For I tell you, unless your righteousness exceeds that of the scribes and Pharisees, you will never enter the kingdom of heaven. [Mt 5:17-20]
Remember that the Pharisees kept the Laws and Commandments - they would not commit adultery, they tithe 1/10, etc. But Jesus demands the more - we have to do the teachings of Jesus too (mercy, golden rule, sermon on the mount ...) because in the Last Day, we will be judged by the words of Jesus.
As for commandments : Jesus : If you keep my commandments, you will abide in my love, just as I have kept my Father's commandments and abide in his love. [John 15:10]
Here we see that Jesus kept the commandments of LORD too ! Jesus even made tassel on his clothes ! and Jesus is supposed to be the model of all mankind. (LORD GOD told the ancient Israelites to make tassels on their clothes, as a constant reminder that they should do LORD's Laws and Commandments.)
Therefore the Laws and the Commandments are not to be abolished, but they must be fulfilled by every Christian. In fact, the main precepts in the Laws is simple : faithfulness (i.e. keeping one's promises), justice and mercy. Therefore keeping them is not burdensome. Moreover LORD GOD will not judge us as the Pharisees did. LORD GOD held David to have done no sin other than that in Uriah [2 Samuel 11,12]
As for "new covenant", if you care to read my webpage "covenant.htm" you may know more. In essence, it is - if we truly believes Jesus, then even if we have broken the Laws and Commandments occasionally (because of weakness, error or ignorance, but not high-handedly), LORD will not take away His steadfast love from us (but He will still discipline us according to His Laws and that could be terribly painful ! High-handed sin has no forgiving, because he tramples upon the blood of Jesus.) According to the Old Testament, if one breaks the Laws and Commandments, he will die.
Now return back to the Book of Mormon. It is not a fiction out of the mind of Joseph Smith. He was a translator only (he had rare gift, he had even written a book, called "Egyptian Alphabet and Grammar" available at Lighthouse Ministry, Utah. LORD GOD gave him gift to understand Maya heiroglyph, improved version from Egyptian heiroglyph). He translated from plates buried on the ground by one Maya people, Moroni. Moroni buried the plates in about the year 420 A.D. Many Maya relics were discovered this century, and those in the Amazon jungle (using Satellite Imaging), only recently, and Joseph Smith died in around 1845 (if my memory is correct), how could he invent things that correlates so well with archaeological discoveries in this century !!
Moreover, the plates have been witnessed by 3 persons - David Whitmer, Martin Harris, and Oliver Cowdery.
David Whitmer has written a book, in his 82, called "An Address to all believers of Christ", you may check it up.
Martin Harris have been interviewed, and reported on the newspaper, and you may read about his interview.
Oliver Codwery's private letters have been published, and you may find it in the internet.
Book of Mormon, as it is a true historical record of the Maya people, provides us with valuable historical lessons, just as the Bible, which is a true historical record of Israelites, provides us valuable historical lessons - one can learn a lot from them - if people broke LORD's Laws, LORD will have them invaded and be carried away as slaves or killed.
This is one reason why I hope Christians should read that book. Moreover, the Maya People were Israelites migrated to America 600 B.C. and as they were extremely good Christians, their records are invaluable to the edification of Christians. (Brother Paul was a good Christian, his letters were terribly good for edification and were collected in the New Testament !)
Mormonism came because Joseph Smith has fallen. He introduced many abominable practices and precepts to his Church LDS. Therefore I hope Christians would NOT learn those "mormonism", but simply read that book.
The main theme of the Book of Mormon is the same as that in the Bible : that people should obey LORD - keep his Laws and Commandments. Those who break the Law will be cursed, and those who keep the Law will be blessed.
This is especially important for people living on the America continent - because LORD GOD has a distinct will on this land - a land of liberty, people who live on this land must serve LORD and keep his Laws and Commandments, or else they will be removed.
Jesus : If any one hears my sayings and does not keep them, I do not judge him; for I did not come to judge the world but to save the world. He who rejects me and does not receive my sayings has a judge; the word that I have spoken will be his judge on the last day.
LORD : Speak to the people of Israel, and bid them to make tassels on the corners of their garments throughout their generations, and to put upon the tassel of each corner a cord of blue; and it shall be to you a tassel to look upon and remember all the commandments of the LORD, to do them, not to follow after your own heart and your own eyes, which are you inclined to go after wantonly. So you shall remember and do all my commandments, and be holy to your God.
Project Guttenburg : (book of Mormon download)