在这句话中，助动词would不是表示从过去某一时间看来将要发生的动作，而是谈论过去经常或总是发生的事。换言之，它表示过去的一种习惯动作，常和often, sometimes等副词连用，可译作“总是，常常”。

参考译文：在最后一幕中，一位狱卒总是拿着一封信上场，然后会把这封信交给那位贵族。

例如：

He would often sit for hours, book in hand.

他常常手不释卷地一坐几个小时。

Sometimes the boys would play a trick on their teacher.

孩子们有时会和老师开玩笑。

He would often climb a mountain when young.

他年轻的时候常去爬山。

After he had finished his work, he would read and study by the fireside.

他做完工作之后，常坐在火炉边读书和做研究。

“Beauty is only skin deep,” my mother would say.

“美是肤浅的。”我妈会说。

区别在于：would表示回顾往事，而used to表示今昔对比，强调现在已经不再 --- 了。

例如：

He doesn’t hate her as much as he used to.

他现在不像以前那样恨她了。

He used to play tennis before his marriage.

他结婚以前经常打网球。（意思是现在不打了。）

People used to think that the sun went round the earth.

人们从前以为太阳绕着地球转。（意思是现在人们已经知道地球绕着太阳转了。）

When I was a boy, I used to like chocolate.

我小时候喜欢吃巧克力。（意思是现在已经不喜欢了）