This article by Aluf Benn struck me as containing important comments by Israel’s defense minister, Ehud Barak:
Speaking at the annual memorial for Moshe Dayan at Tel Aviv University, and in private conversations reported by my colleague Yossi Verter, Barak presented as the casus for the current belli the fact that Hamas “broke the rules” by firing an antitank missile at a military jeep on the Israeli side of the border last weekend, and blowing up a “tunnel with half a ton of antitank explosives that was partly in our territory.”
He implied that Israel could not agree to the new game rules, which in effect created a Palestinian security zone on the Israeli side of the fence that could mean death for anyone entering it. That is what the IDF did on the Palestinian side of the fence, enforcing a “special security zone” there. But what’s good for the goose is prohibited to the gander.
This kind of information helps answer the question of “why now?” (Neither example is about missiles, by the way.)