This is the epigraph from Chapter 58 "Never Again".
So, first part.
Melishi is going to destroy the Voidbringers. Simple enough.
However, we know that the voidbringers have not been destroyed, but enslaved as parshmen.
Part 2
So, in his tent he comes up with or is presented with a different tactic. Something that only Bondsmiths can do. As stated before, we know that the voidbringers were not destroyed, but enslaved as parshmen. So, logically this tactic would be some way to change the voidbringers into parshmen.
Part 3
So, he was too hurried to write it all down, but it was something only the Bondsmiths could do. I haven't thought through exactly what "it was related to the very nature of the Heralds and their divine duties" refers to. My initial hunch is some kind of forceful bonding of the voidspren that is bonded to the voidbringer. That bonding pulls the spren from the voidbringer, turning them into a parshman. Or perhaps something to do with the Storm Father, as he seems vital to the bonding process of both the Knights Radiant and the Parshendi/Voidbringers.
Anyway, it was just something that caught my attention while listening to the audio-book.