请问这句话如何理解？

There were a good many different things.

源于纳尼亚传奇:魔法师的外甥。

不了解这里为何用了a，然后这里的good如何理解。

a good many = many

a good 表示程度，强调数目多、数目大。多用于表示“数、量”的名词之前。比如：

Theygotagooddealofdelightfromtheir children.

他们从孩子身上得到了不少的乐趣。

The living room is large enough fora goodnumber of people.

起居室足够大,可以容纳不少人。

We waiteda goodfifteen minutes.

大家足足等了15分钟。