How is the Book of Mormon different from the Bible?

To understand the differences between the BOM and the Holy Bible, we first must look at these two volumes of scripture within the context of their similarities. So here is what they have in common:

1. They are both volumes of scripture written by prophets.
2. Millions of people study (and believe in) each, though manifestly at least 100X more people accept the Bible than the BOM.
3. They both have similar objectives: persuade people to believe in God and live peaceful/productive lives.
4. In terms of theology and doctrine, most of what is in the Bible and the Book of Mormon is unproveable and must be taken on faith.
5. Both were written over a very large span of time.

Here are the significant points of difference between the Bible and the Book of Mormon:

6. The Book of Mormon contains a consistent theme from start to finish: persuading people to believe and follow Jesus Christ. In the Bible, a similar theme exists in the New Testament, but it's often harder to detect in the Old Testament, and our Jewish friends would presumably conclude that there is no such theme in the Old Testament (Torah/Talmud).
7. The Bible has numerous sections that are non-doctrinal in nature, such as historical, proverbial, and legalistic. The Book of Mormon has elements of these as well, but is mostly either doctrinal on the surface, or contains doctrinal undertones.
8. Nearly all Catholics, Protestants, and Evangelicals believe that the Bible is the word of God and the BOM is not. Nearly all Mormons believe that both are the word of God.
9. BOM prophetic writers frequently make reference to the Bible, especially to the writings of Isaiah. The Bible makes no direct reference to the Book of Mormon, but Mormons believe there is a veiled reference to BOM peoples in John 10:16..."And other sheep I have, which are not of this fold: them also I must bring, and they shall hear my voice; and there shall be one fold, and one shepherd." Mormons believe that Jesus visited the people on the American continent shortly after His ascension spoken of in the Bible.
10. Nearly everything in the Bible takes place in the Middle East. While the Book of Mormon begins in Jerusalem, describing a family that flees the city into the desert, the vast majority takes place on the ancient American continent (long before the term "America" existed).
11. The Book of Mormon was translated from a single collection of ancient metal plates, and all within a single year. The Bible was pieced together over thousands of years and translated by many different people.

The Book of Mormon has a much greater consistency of style than does the Bible, which is much more clearly the work of many authors over a period of centuries. In the Bible, only Mark's Gospel has sentences frequently begin with 'And', whereas sentences frequently begin with 'And' in any book within the Book of Mormon. This consistency seems somewhat unlikely to have resulted from translation, and suggests that the various authors of the Book of Mormon were influenced to adopt the same style as Mark.

In the Book of Mormon many sentences start with an extension through to 'And it came to pass ...': opening the pages at random, I see Jacob 5:25: "And it came to pass that when the Lord of the vineyard ..." and Alma 50:35: "And it came to pass that the army which was sent ..." The Mormon community maintained a surprisingly consistent literary style over many centuries.

The Old Testament never mentions Jesus by name, and passages often interpreted as referring to the Messiah are seen as having other possible interpretations. The Book of Mormon directly mentions Jesus Christ by name more than 500 years before his birth (2 Nephi 20: "... and as the Lord God liveth, there is none other name given under heaven save it be this Jesus Christ, of which I have spoken, whereby man can be saved."

The New Testament is somewhat ambiguous as to when Jesus was born. In the Book of Mormon, 3 Nephi 1:19 tells us that the date of Jesus' birth was unmistakable because there was no night that day, right across the world; a footnote tells us the exact year - 1 AD.

The Old Testament was written in Hebrew, with some Aramaic in places, then translated into Greek, while the New Testament was written wholly in Greek. They were translated into Latin and then various styles of English, including the somewhat archaic KJV English (and into other languages used around the world). The Book of Mormon was first translated in 1830 into the English of the KJV Bible and subsequently translated from English into other languages around the world.

The Bible and the Book of Mormon both have similar objectives: persuade people to believe in God and live peaceful/productive lives. In terms of theology and doctrine, most of what is in the Bible and the Book of Mormon is unproveable and must be taken on faith.

Most theology of Book of Mormon is similar to the Bible's.However, these five distinctive theological positions are Mormon's, I gather:

• The Old Testament prophet Isaiah prophecy about voices that would "whisper out of the dust," are believed to refer to the publication of the Book of Mormon.
• Adam and Eve ( Hava) eating from the forbidden tree, otherwise known as The Fall, is necessary for humans to experience sexuality, and humans' knowlege and redemption: "Adam fell that men might be, and men are, that they might have joy."
• The church should be named the Church of Jesus Christ.
• The atonement of Christ saves unbaptized people including children who die without baptism.
• The death and resurrection of Jesus brings " a universal resurrection for all mankind, regardless of a person’s belief or performance", all people ("both old and young, both bond and free, both male and female, both the wicked and the righteous") will be resurrected with an immortal physical body .

Though I am not a Mormon, I ( now this is a subjective statement, not part of the answer) find Mormon position on children and non-Christians is generous compared to orthodox Christianity's. It is more closer to people general perception of God's justice and mercy.