It can be argued by people that any religion is bat shit crazy.
I endured catholic school from first grade to the end of high school (my parents were not particularly religious, we went to mass every now and then and of COURSE we went on Easter, Christmas and the like. They just believed that due to the fact that it was a private institution, my education would be 'better'. In hindsight, my surviving parent regrets this and even offered to take me out of that school before my senior year, which would have killed my already comatose social life and possibly had a more detrimental effect on Yung Allen) and hated it once I was able to make my own decisions and believe in what I wanted to and what not. However, one of the most eye opening classes I ever took was the last two semesters, entitled World Religions 1 and World Religions 2. It was eye opening and actually really interesting because for the first 11 years of my schooling, there was always a religion class ; Catholicism. However these classes, instead of having, say, chapters 1-3 being from the first settlement of America until the revolutionary war, then a test, then revolution to 1812, test, etcetra, we would learn about, say, Buddhism for a while, take a test on it, learn about Hinduism, take a test, learn about Calvinism... Et all.
I aced the Calvinism test without studying simply because I was already so bitter about the teachings of Catholicsm being rammed down my throat that something that seemed even crazier stuck in my head so much. It terrified me that Calvinism was a much bigger deal at one point in the Earths history, if I remember correctly, it was kind of in vogue the way that Catholicism could be seen in recent memory. I can totally see how someone like Lennie, whose screws weren't even loose but didn't even exist at this point, could go even further off of the rails by fucking with it.
If I remember correctly, there was a really big Calvinism push at some point (centuries? Ago), and it's decline occurred because if you believe that you are already going to heaven (or hell), and there is nothing you can do to change that, what keeps you from being a bad person? If you're a complete and total monster and you fully believe in your heart that whatever you do on doesn't change your pre-booked all expenses paid afterlife suite, why bother doing good? Which is EXACTLY what occurred to Lennie.
In before people say I'm bashing religious folk: do you, I'll do me. Of course the basis for every religion is be kind to others and be a good person, I'm not saying you aren't a good person if you practice religion or believe in a higher power. If you do, good for you. I look at it as if you have green eyes. It doesn't make you less or more of a person or role model.
Tl;dr - I believe in Gos more than I believe in God word is bond