Genesis specifically is packed with common references, can be read in a few hours, and is fairly engaging and accessible as a coherent piece of literature in its own right.
Ecclesiastes is like five pages and possibly the most quoted thing across european cultures. So many literary references and even common idioms come from there.
After that any one synoptic gospel + john + acts will set you up to catch a lot of christianity-specific cultural references. And then revelation imagery comes up a ton in pop culture, music, film & tv.
All of what I mentioned is about the length of a medium-short novel and would set you up to catch probably the majority of allusions to the bible. You'd be missing some major stuff like moses, david & solomon, plus a bunch of misc but influential stories like jonah & the whale, samson etc. But for bang for your buck it would get you pretty far.
https://www.kickstarter.com/projects/adamlewisgreene/bibliot...
Consider a weaker question: if it weren't a lie, why would so many take that to the point of their own death? While most people are usually opposed to lying, if they felt their reason for lying was important enough - and if they're willing to die for it then it must be - they could easily overcome that.
The resurrection of Jesus Christ is a dividing point to all humanity, and there are many willing to die on either side of the fence. While it has been contested many times, there is no definitive proof that Jesus was not resurrected, and there is pretty solid evidence that Jesus did die on the cross (as opposed to old age or some other natural cause). We also know that the Jewish leaders at the time of Jesus were furious at Christianity, and had a serious campaign to destroy and discredit it, yet it survived. You'd think that with their financial and people resources, they could have recovered a body or exposed Jesus as a fraud.