Reading the books is not a prerequisite from the game. You understand that there was a war between humans and forerunners, and that the forerunner is now your enemy. that is all you need to know for the game. Clearly, you understood that there was a human-forerunenr war, so I don't see the problem. The books merely act as backstory for the interested party. they are certainly not necessary to understand the game, and really have nothing to do with it. although some of the characters from the game appear in the books, these stories have almost no relevance to halo 4.
The Halo universe has always been a mysterious place. We have never truly understood introduced concepts until later games. Why is it so bad that the human-forerunner war is mysterious to you? Mystery is what drives this franchise.