1)
To what should they listen?
1.
Rashi: They should put to heart "Mi Nasan li'Mshisah Yakov" (24).
2.
Radak: This rebuke.
3.
Malbim: Those who bring a proof from the cause to the result - who will 1isten, and bring a proof from the result to the cause?
2)
Why does it say "l'Achor"?
1.
Rashi citing Targum Yonasan: It is what will happen to them in the end. Every l'Achor in Tanach is what will be.
2.
Malbim: This is bringing a proof from the result to the cause.
