1)
Why does it say that they are Chachamim in their own eyes?
1.
Radak: They think that they are Chachamim and wise. When Nevi'im tell them 'this is the good path - go on it, and veer from the bad path', they say 'no - rather, the path that we are on, it is good. We are wiser than you to recognize good and evil!
2.
Radak citing his father: They are Chachamim to do what is straight in their eyes, and clever to fix [matters to be] like is proper in their eyes. This is like "Chachamim Hemah Lehara" (Yirmeyah 4:22).
3.
Malbim (20: Cholim rely on what healthy people tell them, that this is light or sweet. These people do not heed the wise.
