A piercing rebuke is directed at the people, drawing a sharp contrast between the spiritual state of Israel and the rest of the world. Through the striking image of a wife betraying her husband, the people are told to bring their celebrations to a halt. Because of their unique relationship with God, what would normally be a time of joy must instead become a period of deep soul-searching and mourning. They are strictly forbidden from experiencing sudden joy or celebrating good news and success in the manner of the surrounding nations [מלבי״ם].
The primary approach among commentators is that while the nations of the world have never abandoned their beliefs and can therefore celebrate freely, Israel received the Torah and then betrayed God. Consequently, it is inappropriate for them to rejoice even during normally happy occasions like weddings; instead, they must mourn their sins and the many blessings they have lost [רש״י, אבן עזרא, רד״ק, מצודת דוד, ביאור שטיינזלץ]. Other perspectives highlight a deeper spiritual divide. The nations are subject to the forces of nature and astrology, naturally rejoicing when their luck improves. Israel, however, is bound to God in a direct marriage, and straying from His care reduces them to the level of an unfaithful spouse [מלבי״ם]. Furthermore, their joy was never meant to be a physical indulgence or a casting off of restraints like the nations, but rather a spiritual expression of gratitude to God [חומת אנך]. Facing the reality of an impending exile, the people must sit in sorrow and worry, making it entirely unfitting to celebrate while watching other nations enjoy the fruits of their land [אברבנאל].
The core of this betrayal is compared to the act of prostitution, where the people have fallen in love with the illicit payment given for such acts [רש״י]. This love for a prostitute's fee manifested in practical ways: the people chased after other nations to beg for help and basic survival [מצודת דוד, מלבי״ם], and they credited their agricultural abundance and wealth to local idols rather than to God [ביאור שטיינזלץ].
The focus of this sin centers on the threshing floors, the very places where the grain is gathered [מצודת ציון]. This perfectly continues the metaphor of unfaithfulness, as it was common for a prostitute to visit threshing floors to collect grain as payment for her deeds [רש״י, מצודת דוד]. Beyond the metaphor, there was a harsh physical reality to their actions. Instead of offering their required tithes to God from their harvest, the people would bring gifts to idols right there at the threshing floor [אבן עזרא, אברבנאל], operating under the false belief that these statues were the true source of their grain [רד״ק]. Tragically, it was precisely during these times of plenty, when the threshing floors were overflowing and the economy was strong, that the people turned their backs on the good they had been given and embraced idol worship [רד״ק].