A painful cry echoes from God to the nation, mourning an illogical betrayal. It is the deep pain of watching a loving, long-standing relationship cast aside in favor of a hollow illusion. This historical plea focuses on the early generations of Israelites. As soon as they entered the land of Israel, they began to engage in idolatry [רד״ק]. In doing so, they entirely forgot the immense kindness God had shown them. He had brought them out of Egypt, guided them safely through a desolate wilderness filled with dangers and venomous snakes, and settled them into a good, fertile land, which they then defiled with foreign worship [צאינה וראינה].
The situation is viewed through the psychology of abandonment. Typically, a person leaves one path for another for logical reasons: they find a flaw in the old way, discover an advantage in the new one, or find the new path easier. Because of this natural human tendency, God questions what possible flaw or injustice the ancestors could have found in Him that would cause them to walk away [מלבי״ם]. The severity of this abandonment is compared to the deep disrespect of turning one's back and walking out of a synagogue while the Torah scroll is open and being read to the public [צאינה וראינה].
Instead of remaining close to God, the people chose to chase after emptiness. The primary approach among commentators is that this refers to idolatry and foreign gods, which are entirely empty, lack any real substance, and offer no actual benefit. Following these idols was an act of pure foolishness, as the people actively chose to believe in things they already knew had no real value [ביאור שטיינזלץ].
The tragic result of this choice was that the people themselves became empty and devoid of substance. This reflects a spiritual principle of measure for measure. A person who holds fast to God, who is eternal, gains true existence and eternity for themselves. However, a person who chooses to attach themselves to emptiness loses their very essence and becomes empty as well [מלבי״ם]. As a direct consequence of becoming empty, the Israelites lost their national strength, and their rule was humbled to the dust [מצודת דוד].