Many believe that Putin has emboldened the Russians and encouraged them to rebel by a number of his actions. The first was taking over Crimea. The Second was amassing troops on the Ukrainian border. The third was warning the Ukrainian government not to harm Russian citizens. Putin has also added that they will have no option but to send their troops in to protect Russian citizens.
The Ukraine has already accused Russia of having officers assisting the rebels. Observers believe that Putin wants to annex eastern Ukraine or have an eastern section of Ukraine break off and become a pro-Russian independent republic. It is believed that he is simply looking for the right time or a good enough excuse.
One excuse would be the alleged shelling that allegedly took place July 14th. Another would be violence or alleged violence against russian citizens. They could also be waiting until there is so much violence and destabilization that they must go in to bring peace to the region. Of course he can do what he can to make sure that destabilization happens in the first place. By warning the Ukraine not to harm Russian civilians he may actually be simply trying to tie the hands of the Ukrainians. If they fight the rebels too agressively they risk giving Putin the excuse he is looking for to send troops into the Ukraine.
The longer this drags out the more likely it becomes that Putin will use the reasoning that he must stabilize and bring peace to the region. He would then hold some kind of an election to determine the fate of eastern Ukraine. If the Ukrainian side becomes stronger Putin may decide it's time to go in sooner. Either way way the Ukraine is in a difficult spot. Their best bet is to turn the tide of the people against the Russian rebels and defeat them through a propaganda war that would require less fighting. That would be there best chance for a positive outcome.