It's a provisional ending. It's not a rhyme word, and so it doesn't constitute the end of a unit of sense as a rhyme word would in most heroic couplets.

它不是真的结尾，不是韵脚，因此它不像大部分英雄双韵体中的韵脚词一样,标志着一个意思表达的完结。

耶鲁公开课 - 弥尔顿课程节选

And so in Milton's verse here, sense or meaning is variously drawn out from one verse into another. Sense, the very spirit of meaning, is infused throughout an entire line rather than being singled out and separated or segregated to the end of the line in the form of the rhyme word.

弥尔顿的诗句里，感觉或意思在句与句,之间传递，感觉，意思的灵魂,贯穿于整句，而不是被分离出来,以韵脚词的形式放在句末。

耶鲁公开课 - 弥尔顿课程节选