As far as *why* Russian has this is incredibly interesting to me.

The roles you see labeled by the Russian endings are roles that make up the fabric of how a series of words is to be understood.

The dog bit the cat.

In English, you know that the dog is not hurt, because it did the biting. You know this because you can tell it is the subject (that, which does the verb) of the sentence. You can tell it is the subject of the sentence because of the order in which the words came -- flip the words, and the meaning becomes the opposite.

So for English - Word order determines sentence roles.

However for Russian, the endings give all the necessary information about grammatical roles, meaning that the word order is no longer restricted. This is a fundamental aspect of human language that has fallen deep into the background in English.

Word order was out of a job, and in language, nothing is ever useless, so the word order then gains magical uses that even further add to the possible information a person can relay with a set of words. Thus, what in English might be a change in voice tone, a gesture, a glance, or a choice of word - can sometimes be dealt with by just changing the Russian word order.

Because of all this you will see word orders in Russian that can be anything from the opposite of what the English uses (though with the same fundamental meaning), or even word orders that are altogether foreign to English.
Я тебя люблю
Я люблю тебя
Тебя люблю я
Can each have a theoretical reason and added meaning based on the order, though they all mean at heart "I love you"

"Спит стальной твой дракон" - Forgive the odd example, it's from a metal song.
Sleeps steel your dragon - word for word translation, in the same order
Your steel dragon sleeps.
What's cool here is that Russian can even move around possessive pronouns [my, your, his, its], but in English, these words must *always* come in the beginning of the noun's trail of ducklings. (For this analogy: last in line = first word you hear)
"In this our hour of need..." is really the only way it is any different

One of my favorites is that if an adjective follows a preposition, the adjective's and preposition's noun can be elsewhere in the sentence.
Я на твоей останусь стороне
I on your stay side
Here, because the word "your" matches (audibly and visibly) in case with "side", the word "side" no longer has to remain attached proximally to its governing preposition. It's like a preposition demands a noun of a particular case to follow directly after, but it will settle for the noun's adjective.
(Also, conjugation tells you that the subject of "stay" really is the "I" you read a second ago)

Russian essentially wraps up groups of words with beautiful little bows.
A prepositional phrase includes the preposition (on, at, for, in, with), its object (a noun), and any adjective or adverbs modifying that noun or its modifiers. This phrase is inherently a whole unit, that can be moved around sentences. In English, you know that a prepositional phrase has come to an end through the means of a messy process of discerning when that preposition's noun has arrived. In Russian, the case system neatly labels everything that belongs to whichever preposition that it does, and labels everything as to how it relates to the verb of the sentence. The verb is the king.


The free word order is also conducive to a writer being able to intentionally design which ideas come first in order to smoothly get across complex ideas (or just complex sentences).



Imagine tetris, but in Russian you get to choose which block you use next.