Not sure if it violates forum rules but I just found out that there are WH40 books for sale on humble:https://www.humblebundle.com/books/horus-heresy-warhammer-book-bundleIf the post is in violation please take it down :)
Yeah it's a pretty amazing deal, I jumped on it right away. The first 15 books in the Horus Heresy along with 3 audiobooks and some extras for 15 dollars is fantastic. I was avoiding it because there's so much to catch up on, but with a deal this good I couldn't resist. I just want to note that Macragge's Honour follows immediately after Know No Fear which is book 19 in the Horus Heresy. Funny thing too, I was debating whether I should buy it or not and then this bundle popped up. So much money saved! To spend on more Warhammer books haha.
I would say, the best way to get started with 40k fiction is to get a hold of some of the omnibus editions. For example, the Eisenhorn & the Ravenor omnibus are both great introductions to the Inquisitorial side of the genre.
It's pretty relevant, and a very good deal, a nice set of Black Library ebooks for those who are interested in that era. We'd love to see more people reading W40k!