The prophet shifts into a new phase of his rebuke to the Israelites. Having already detailed the sins and terrible acts of the earlier generations during their time in the desert, the focus now turns to the severe wrongs committed the moment the people entered the Land of Israel.
This transition marks a clear escalation in their wrongdoing. The primary approach among commentators [מלבי״ם, רש״י, רד ק ואברבנאל] is that the people had already failed three times before crossing into the land, making this the fourth major sin, which took place after they had finally settled there. Alternatively, this stage of the rebuke serves to draw a direct line between the past and the present, pointing out that the current generation is acting in the exact same sinful manner as their ancestors did [מצודת דוד].
The specific nature of this failure was far from an ordinary mistake. It involved actively insulting, shaming, and blaspheming God [מצודת ציון, ביאור שטיינזלץ]. The people acted out of direct rebellion and crime [מצודת ציון]. They did not hide their actions, but rather sinned publicly, intentionally, and with deep contempt. It was a complete denial of God, carried out with sheer arrogance and open defiance [מלבי״ם].