Q:

What does "they" do in "Though wise men at their end know dark is right, Because their words had forked no lightning they"?

Below are two lines from a famous poem by Dylan Thomas:

" Though wise men at their end know dark is right,
Because their words had forked no lightning they 
Do not go gentle into that good night."

I can sort of understand what he tries to imply, but I am wondering what does they  do or mean there?
Does it related to the next line? That might be the case. That's the only thing that comes to my mind. In this case, is that punctuation correct though?

A:

"They" is just the subject of the clause in the next line. The phrase "Do not go gentle into that good night" is imperative in other places in the poem. Here it is declarative.
"...because (reasons), they do not go gentle into that good night."

