A long sentence

[HaraKiriBlade]

In truth, all through the haunted forest there could be nothing more frightening than the figure of Goodman Brown. On he flew among the black pines, brandishing his staff with frenzied gestures, now giving vent to an inspiration of horrid blasphemy, and now shouting forth such laughter as set all the echoes of the forest laughing like demons around him.

Forgive me for the lame title for this thread, but I could not come up with a better one.

Anyways, that's not the concern. I got the gist of the sentence, but there are a few things in the sentence I'm not familiar with. Could you explain why the boldened parts are there in the sentence?

Much appreciated!

- HKB

[Tdol]

On he flew- inversion of 'he flew on' to suggest he continued his flying. You could get rid of the preposition if you wanted.
as set = which caused the echos to laugh like demons around him

[BobK]

I'll add a bit to Tdol's comment:

On he flew- inversion of 'he flew on' to suggest he continued his flying. You could get rid of the preposition if you wanted.
The inversion is for emphasis - it suggests that Goodman Brown was vigorous/energetic/unstoppable.
as set = which caused the echos to laugh like demons around him
...and what it's doing in the sentence is completing the idea started by 'such' - 'laughter such as [of the sort that] set...'

b