My thought on this change of strategy for Russia's army is that they realized their mistake of spreading their forces too thin in a multi-front war. So they're going to consolidate everything in the east, and hope to use a concentrated, overwhelming force to push back the Ukranians. That's the type of fighting that Russia is comfortable with, and it puts Ukraine at a bit of a disadvantage.

This means the war will be a lot longer than originally planned, but Russia will do a slow push until they've taken the rest of the country. My guess is they'll eventually get to Kyiv, and they'd like to have given the Ukranian army enough losses by then that they won't be as formidable as before. I can't imagine Putin accepting a withdrawal from Kyiv and settling for only the eastern part of the country - not after he said their aim was to take the whole country.

I could be very wrong and Russia will stop after they take the east, but I have my doubts.