The Bible is one of the oldest books that is still present and read in modern society, when you consider it from the point of oldest authorship. Of course, this is somewhat misleading, because in truth the Bible is not actually one book. It is (by Protestant standards) 66 books, although even that isn't entirely true because not all 66 "books" are distinct. Many people reasonably consider the first five books of the Bible (called the Pentateuch for that reason) to be actually a single book. Certainly they were intended to be read as single unit. Similarly, the books of Samuel, Kings and Chronicles were written as single entities but split into two parts and subsequently called two "books". But with all of these details aside, the Bible consists of at least 55-60 separately written, distinct books.
So the first thing the reader should understand is the somewhat fractured nature of the Bible. Estimates vary on the date of the oldest book, but even the latest estimates put it around 600 BCE, while the earliest estimates for the youngest book, Revelation, put it around 70 CE. So that means that from start to finish, there is at least a 670 year gap in the writing of the modern Bible. By conservative standards, the oldest books were written around 1600-1500 BCE and the youngest were written around 90 CE, putting the gap at an even greater 1600 years. Considering that we are only 2000 years past the events of the New Testament (NT) itself, it should be astonishing to think that the oldest events of the Old Testament (OT) are nearly as far back in history to the New Testament authors as the New Testament is to us. Clearly the OT (also known as the Hebrew Bible) was considered holy scripture to the NT authors, and indeed there are many places in the NT where the authors quote the OT as scriptural references to prove doctrine or prophetically reference modern events, much like modern theologians debate over NT scriptures. Even the smaller date, 670 years, is roughly three times the duration of the United States as a nation.
Estimates vary on the number of authors. While the Protestant Bible contains 66 books (of which perhaps 59 are distinct), the authorship of these different books is highly debated. For my part, I'm going to generally assume that the author is the self-referenced creator of each book (so, for example, the author of the book of Isaiah is Isaiah himself, as described in Isaiah 1:1). Since most (but not all) of the books in the Bible make reference to their own author, this resolves the authorship of most books and gives you a rather high number of authors (at least 20-25 distinct authors). So again, this shows that the Bible is highly fractured in terms of both date and authorship. Therefore one must expect stylistic differences, cultural differences, and language differences to appear in the various books. One can also identify certain theological differences and in some places the same story is told more than once and with differences between the different versions.
But at the same time, all of these differences serve to highlight even more the surprising similarity between all of the books in the Bible. There are thematic elements that run all the way from Genesis to Revelation, messages about the human condition, about the demonic opposition faced against man, and about the nature and purpose of life itself. Obviously when dealing with such weighty subjects, no single message or posture will please everyone, and it will certainly spark a lot of controversy, as has been the case for essentially the entire duration of the Bible itself. Ironically, many of these historical controversies are documented in the Bible itself, but by no means have they slowed down. It's fairly popular these days to say that we (as people) are more divided than we have ever been, but if one reads about the life of Jeremiah, about kings Rehoboam and Jereboam and the division of Israel, or about the divisions brought about by the emerging Christian sect of circa AD 30, one can see that such divisions have existed for thousands of years and our time is not unique in that regard.
At the end of the day, perhaps the doctrinal and thematic unity of the Bible can serve as a greater example of the unity possible, and desirable, in human society, resolving itself in the redemption of human existence through the Passover sacrifice, Jesus Christ; that in his sacrifice, we might find peace with God and peace with each other; that even if every other difference were to remain, at least we could learn to appreciate each others' perspectives and find the beneficial synergy of differences as described in 1 Corinthians 12. Regardless, I will discuss all of these topics at depth in the proper chapters of study.