1)
Why did Hashem forbid Yirmeyah to go to the banquet hall?
1.
Rashi: This explains why He said above not to go to Beis Marze'ach (according to Rashi's first Perush there) - for Hashem is eradicating Simchah from here (verse 9).
2.
Malbim: You may not go even to sit with them, to honor them via your company, without intent for Simchah, and not for your needs, to eat and drink.
