Israel calculated that killing Hamas's military wing commander Ahmed Jabari and stepping up Israeli military operations would “restore deterrence,” going back to a post-Cast Lead situation of relative quiet. It seems Israel decided to use military force to weaken Hamas's military arsenal while also hitting its resolve to fight.
The current military operation can arguably accomplish both of these tasks (the first one much more easily than the second). However, while Israel has a clear right to protect its citizens, the question that needs to be asked is: Are the costs of a further escalation and of a possible ground operation worth it for Israel, and how much time can it buy?
The first obvious cost of the ongoing escalation rests within the civilian population in both Israel and Gaza, who are paying directly for the resumption of major hostilities.
Israel appears to be confident it can bear the military costs of the operation. But this assumption is largely shaped by the awareness that the conflict is unlikely to expand to a region-wide war. Iran is dealing with crippling sanctions, Syria is in the midst of a civil war, and Hezbollah’s power has been diminished by its siding with its Syrian patron, the Bashar al-Assad regime. So it is unlikely that any of these parties will get directly involved in the fighting in Gaza.