这是一个由介词短语引导的完全倒装句：

At the heart of the unease about these earliest works of literature were two fundamental questions.

= Two fundamental questions were at the heart of the unease about these earliest works of literature.

1. 倒装的原因和目的是：questions 后面是冒号，引出较长的同位语。

2. 句子的主语是：two fundamental questions，所以用复数动词were，跟the heart 无关。

3. at the heart of = at the center of “位于…的中心/核心”，前者可以表示抽象意义。介词短语作表语。

The very reason that cliches so easily seep into our speech and writing - their insidious memorability - is exactly why they played such an important role in oral storytelling.

这个 is 对应的主语是 reason 吗？—— 是的，看红色部分。