"For the leaders of this people cause them to err; and they that are led of them are destroyed.
If that "therefore" was not here we would not know what follows was there for. This "therefore" is in part conditional, based on actions that precede it. Let's read on...
"...The Lord shall have no joy in their young men, neither shall have mercy on their fatherless and widows: for everyone is an hypocrite and an evildoer, and every mouth speaks folly. For all this His anger is not turned away, but His hand is stretched out still" (Isaiah 9).
Oh my soul!