Marx's original title for this was "The Communist Confession of Faith" but that would've been too honest so Engels had him change it.
Again: it's a religion--not merely a "political/ economic system."
Discussion
Marx was actually raised in a Christian home but early on appears to have become a Satanist, as documented in this book:
I haven't read it yet, but I have heard some interviews with the author that are persuasive. If you look at the fruit of communism, it appears to have been a key tool of Satan...