The aim is to strengthen Nato's defensive position, minimise / undo Ukraine territorial losses whilst avoiding WW3 / nuclear war.
As much as we want to punish Russia and its allies for this war, we don't want to drag European populations into another large war / create a radioactive hellscape. One reason being, we are not armed enough to fight on multiple fronts and still contain other threats.
The unfortunate reality is that there is little chance Ukraine will regain a significant portion of its territory given the current state of the counteroffensive. This is why Zelensky is pushing hard for NATO membership, he hopes there is a slim chance that Article 5 would be invoked upon Ukraine joining and other European countries would become directly involved in the war, which is a risk Europe doesn't want to take. Duda himself just alluded to this
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