1)
Why did Hashem swear?
1.
Malbim: This is a decree with a Shevu'ah (it is never retracted).
2)
Why will they not call Hashem's name?
1.
Radak: Since they do not heed what the Navi tells them in My name, their mouths should not mention My name.
2.
Malbim: They will truly forget Hashem, until they will be like total Nochrim in every way.
3)
Does this apply to every Ish Yehudah?
1.
Radak: It applies to most of them. There were Tzadikim among them, e.g. Yirmeyah and Baruch ben Neriyah.
