Yet he could not tell anyone about his theory as the powerful Christian Church would have punished him for even suggesting such an idea.

这个问题不难理解。在as 引导的原因从句中，for even suggesting such an idea 相当于一个虚拟条件句：if he had even suggested such an idea

全句可理解为：

the powerful Christian Church would have punished him if he had even suggested such an idea.

这个句子表达的意思，是与过去事实不符的假设：事实上，他并没有（没敢）提出这样一个观点，基督教也没有惩罚他。