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human
ELI5: Dune by Frank Herbert

I've just finished reading Book 1 of Dune, which concludes shortly after Duke Leto's death, and I've found myself with more questions than answers.

I'm going to continue reading, but I can't help but feel that I am missing something. If there are any fans of the book here, please take a look at my questions and tell me if they are eventually answered, because I am quite confused.

Why does the Emperor want Leto dead in the first place? From multiple accounts, it seems they are (were?) good friends. I'm guessing political intrigue, which is the most sensible, but this never gets touched on! I have no idea what is behind the motivation of the central plot of Book 1.

More importantly, why is the Emperor so invested in Leto's death that he is even willing to commit Imperial troops? From what I understand, the Great Houses and the Emperor are two separate and powerful political bodies right, so what is so important that he is willing to put his personal stamp on the death of a leader of a great house?

What the heck is spice? 

What exactly happened in the Buterlerian Jihad?

Was the Bene Gesserit actually able to implant the entire workings of a religion into Fremen culture?
gpt
The major parts of the economy in the Dune universe is controlled by one super-corporation called CHOAM (Combine Honnete Ober Advancer Mercantiles) which in turn is ruled by the Emperor and the Great Houses (through the Landsraad). 

House Atreides is up-and-coming in the Landsraad and the Emperor feels threatened and recruits House Harkonnen to make a indirect power-grab of CHOAM and through that the spice trade.

The importance of spice is two-fold: the most popular use is to become very old so it's used by the rich (such as the Great Houses) and commands a very high price. The Bene Gesserit also use it as a means to delve into past memories of their ancestors.

The original series is a bit vague on the Butlerian Jihad but the aftermath basically boils down to "We relied too much on computers a long time ago and it ended badly and we will not do that again".

Possibly slight spoiler, the Bene Gesserit doesn't implant "entire workings" but more of a framework to further their own future interests.

I think I've been a bit vague but that was on purpose. Please read the rest of Frank Herberts Dune novels. Frank Herbert wrote "big", there where wheels within wheels and deep plots but the characters motivations are still central. 

There are many like me that feels that the  prequels and sequels that his son Brian Herbert and Kevin J. Anderson wrote aren't that good. Basically it goes from "what, that can't be right?" to "wtf, this is what you came up with as an ending???" for the last book.