Some pieces of the Bible are repeated (several times even) without changes. Let's look at the book of Leviticus, especially chapters 13-16, which concerns laws about leprosy, mold, and bodily discharge. This is a real tautology feast (in the rhetorical sense). Worse is Numbers 7, which repeats the same details of the offerings made by each of the twelve tribes twelve times.
Why would the author be so repetitive?
The bible was written in a time of a primarily oral culture. Repetition is often used for emphasis or to drive home a point (as Seeker of Truth mentioned), and to make things easier to remember. So important things were repeated a whole bunch of times in slightly different words to make it easier to remember. Even if you didn't remember it the first several ways they said it, if you hear the same message over and over it will sink in.
However, in some of these passages you point out, the repetitiveness is more an artifact of these books presenting a historical record, in a detailed and factual way. That passage from Numbers 7 almost reads more like a transaction register...there are multiple ways to account for this.
One, building the tabernacle, a home for God on earth, was a really big deal...so important that they were quite meticulous in documenting what God's instructions were about building it, and how Isreal did on their quest to implement God's directions (and of course, it's just about always significant when there's a deviation from the usual pattern or someone didn't follow through correctly. So what we're seeing here is every tribe followed through and sacrificed all the required sacrifices as required, along with details about who did what when.
Secondly, it reads more wordy in English in general, because in many cases a hebrew word becomes an entire phrase in English because we don't have a consise word to accurately describe the same concept. Not to mention, Hebrew uses a lot of prefixes instead of joining words (so "and" and "for" and so on are not seperate words) so there's less words overall. So if you spoke Hebrew, and read the same passage in Hebrew it would be shorter and sound a lot less redundant. A typical example phrase from Numbers 7, "And for a sacrifice of peace offerings" instead of being 7 words becomes only 2 words in Hebrew (וּלְזֶבַח הַשְּׁלָמִים, or transliterated, ûl'zevach haSH'lämiym).
Third, in some cases, it's hard to read because of the formatting chosen by the particular bible pulisher. Much of Numbers 7 looks like tabular data. If it were lined up into nice neat columns where "5 male goats" lines up neatly for each of the 12 tribes it would be much quicker and easier to realize the words are the same for each tribe, than when each tribe's sacrifice is presented as a multi-line paragraph.
As far as Leviticus 13-16, this portion is pretty much a medical manual for the priests. You might compare it to sitting down and reading the physician's desk reference today. It's going to be very detailed, because it's about how to diagnose whether a particular skin disease is of a leperous nature or not. Lepers had to be isolated from society, so it was a very serious condition, and differentiating harmless conditions from serious ones is kind of important, ya know? So they take their time in being very detailed in describing similar ailments and what symptoms are or are not indicative of leprosy, and how to disinfect the home of a leper and atone for their sin and so forth. Kind of one of those things that's not super-exciting in our day to day life where it doesn't seem very relevant, but if you had someone around you with a contagious skin disease, you'd probably suddenly want to read in detail to avoid it spreading to you ;-).
Additionally, you didn't specifically mention this in your question, but I imagine you noticed significant parts of Exodus and Leviticus are repeated very closely in Deuteronomy. That specific mass repetition is in large part because the end of Exodus and Leviticus were a historical record of Isreal right after they left Egypt. But then as we learn about in Numbers, they weren't obedient to God and spent 40 years wandering the desert, until almost all of the previous generation had died of. So Deuteronomy is in large part Moses's "final speech" to this new generation of Isrealites just before the enter the promised land, as most of them hadn't been born when this important message from God was delivered the first time.
Sergey, you ask a very valid question, especially given what is stated in Matthew 6:7 about not using meaningless repetition ( “And when you are praying, do not use meaningless repetition as the Gentiles do, for they suppose that they will be heard for their many words." Mt. 6:7, NASB). Given this teaching, we can know that the repetition in Leviticus and Numbers is not meaningless.
So what is the meaning?
As humans we have a bad habit of not applying to our lives that which is instructed to another. In the passage mentioned in Numbers, God is making it abundantly clear that this instruction about making offerings applies the same to all of His people. There is no one that is guiltless of sin and there is no one who is exempt from needing to have their sin covered by a sacrifice (that includes you Judah and Benjamin and Gad and Asher... and so on). Sometimes the Bible is repetitive because God understands our nature and He makes certain that we all know that it all applies to us all.
There is also repetition for the purpose of really driving home a point. We still do this in our society today...we repeat something that is really important so that we can make certain that those listening understand that a certain point really matters. In Leviticus, there is a lot of talk about how to be pure from sin, and it is repeated... a lot. God really wants us to understand how important it is that we live pure lives (which none of us have as we are all guilty of sin, Romans 3:23). Since none of us are free from sin, we need to understand that there is a way to be purified of our uncleanliness. In the old covenant it was through these sacrifices and cleansing processes, and now that we are under the new covenant it is through the sacrificial blood of Jesus Christ. This is repeated so that we understand the vital nature of what God is instructing us.
Leprosy is representative of sin, which in the Hebrew Bible made one "dirty" (unclean). For example, the "tautological" repetition of leprosy and its signs in the house formally occupied by Canaanites (in the latter half of Chapter 14), while speaking to mold or persistent mildew, may also speak to the possession of the house by unclean spirits. (Nota Bene: such "mold" attaches itself to stones or other objects within the house or on its walls, and therefore had to be removed or "exorcised" in order to eliminate the uncleanliness from the house.) The process and procedures for the identification of leprosy are therefore "tautologically" repeated because leprosy (at the time) could be confused with other manifestations that appeared similar, but were entirely different. "Leprosy" was therefore something very serious. For example, while the affliction by unclean spirits may exhibit itself in mental disorders in people (for example, King Saul's acute paranoia), not all mental disorders have their basis in unclean spirits. Manifestations can appear to be similar, but are in fact entirely different.
The repetition of the tribal gifts at the dedication of the Tabernacle has an important purpose. As pointed out by Rav Shlomo Breur, as quoted by Rav Yisachar Frand, the Torah could have told us that "Nachshon brought these things as a gift and all the other tribes gave the same thing." But it didn't because when describing gifts it is not what was given, but how it was given. Every gift is unique for the giver. Donald Trump could give you $1000 and I could give you $1000, but I can assure you that a $1000 gift from me is a much bigger statement than the same gift from The Donald. Rav Frand explain that this "is what the Torah is telling us. The fact that the Torah has to repeat 12 times what the Princes gave, perforce means that these 12 gifts were not exactly alike. Each Prince put his own special stamp on his gift, making it unique and special." Rav Frand compares this, also, with the Song the Israelites sang after the parting of the sea. Although 600,000 sang the same tune and the same words, each individual was singing about his own personal revelation and experience, thus each one sang, "This is MY God," rather than "our God."
I also heard a lovely interpretation, I believe from Rabbi Gedaliah Anemer, zt'l, and also related by Rossaly Saltsman in her book Portion of Kindness, pp 172-73, who said that after the first gift, the next tribe (Issachar) had three choices -- they could give more, they could give less, or they could give the same. If they gave more it would look like "oneupsmanship." If they gave less, it might look like they were ceap. But by giving exactly the same as Nachshon and his tribe, none of the other tribes were placed in an embarrassing position. The Torah acknowledges this kindness by Nathaniel, the Prince of Issachar, by listing each tribe's gift separately.
As for the descriptions in Leviticus, I would disagree that they are necessarily repetitious. Each word holds importance, believe it or not. Consider the case of the metzorah (sometimes translated, incorrectly, as leper) -- a person who has the spiritual illness caused by the act of gossip. (See, e.g. Numbers 12 regarding Miriam's bout with the disease.) Leviticus 13-14 does go into great detail about how the priest diagnoses the disease and what a huge pain in the neck it becomes. The disease infected his body with nasty sores and even infected his personal belongings and his home. The metzorah would be exiled out of the community proper until the disease was healed. Oy! But there is a lesson there. Just as the priest can ruin the metzorah's day with one word -- "tamei!" ("impure!"), so can one word of gossip ruin someone else's life. If we had this sort of disease today, much of what we can find on the internet and talk radio would be gone.
The answer is that the entire Bible consists of literary architecture. The Book of Numbers, for instance, contains seven symmetrical "cycles," and each of these contains seven "cycles," each of which contains seven stanzas, each of which contains seven lines. Viewed in a linear fashion, it looks like DNA. Viewed side by side, it looks like the weaving of an ancient rug (like this).
I did an analysis of Numbers a few months ago, inspired by a comment on the repetition in exactly the passage you mention. If you are interested, you can find them here.
This explains why the architectural descriptions are so long -- the text itself is architectural. We also find this literary architecture in the New Testament. It explains, for instance, the length and repetition in John 17. The Book of Revelation is laced with these structures like brandy in a Christmas pudding!
Am currently working through the epistle to the Ephesians, which contains exactly the same Covenant-literary structures (here).
The basic shape of all these structures can be traced back to Genesis 1, which is a 7 x 7, 7 stanzas each with 7 lines.
