Compelled to fulfill the King's decree

בפסוק ויקם העם כו'.

On the verse "And the people rose up…"

The Sefas Emes takes up the verse describing how the people rose to gather the quail.

ויש לתמוה שמצינו בכל המקומות כשחטאו בנ"י וכעס עליהם הקב"ה נתחרטו מיד בתשובה ובכאן נאמר מקודם עד אשר יצא מאפכם והי' לכם לזרא ואעפ"כ אח"כ אספו להם השלוים והלא ידעו כי לא לרצון יהי' להם.

And one must wonder: we find in all other places that when Bnei Yisrael sinned and HaKadosh Baruch Hu was angry with them, they immediately regretted and did teshuvah; yet here it was said in advance, "until it comes out of your nostrils and becomes loathsome to you," and even so they afterward gathered the quail for themselves — though they surely knew it would not be favorable for them.

The difficulty: normally Bnei Yisrael repented at once when Hashem showed displeasure. Here, although forewarned that the quail would become repulsive and bring punishment, they still went out and gathered it — knowing it would harm them. Why?

ואפשר שכשאמר השי"ת ואכלתם בשר כו' הי' זה חיוב שצריכין בע"כ לאכול ולקבל העונש.

And it is possible that when Hashem Yisborach said "and you shall eat meat…," this was an obligation — that they were compelled, against their will, to eat and to receive the punishment.

The Sefas Emes suggests that Hashem's words "you shall eat meat" were not merely an offer but a binding decree: they were now obligated to eat and thereby to undergo the consequence.

ולכן הוכרחו לקיים גזירת מלך:

And therefore they were compelled to fulfill the decree of the King.

So they were not acting out of stubborn craving in defiance of teshuvah; rather, once Hashem had decreed it, they had no choice but to carry out the King's decree, even knowing it would bring punishment.

Summary: Normally Bnei Yisrael repented the moment Hashem showed anger, so why did they gather the quail despite the warning that it would become loathsome and bring punishment? The Sefas Emes answers that Hashem's "you shall eat meat" had become a binding decree — they were compelled, against their will, to eat and receive the punishment, fulfilling the King's decree rather than acting from unrepentant desire.