We get so bogged down in the daily stream of atrocities committed by Israel that it's easy to lose sight of the big picture.
At the end of the day the reason why it matters so much, besides it being an affront to our most basic humanity, is because whatever we collectively let happen - or not - will define the fundamental structure of the international order for decades to come.
Why, and how?
The most important thing to remember about the period we're living in is that we're in a transition between world orders. We're exiting US hegemony - it's over already - and entering an new order.
Such transitions happen rarely, once a century or so. The last time was the end of the Cold War when we transitioned from a bipolar world order to US hegemony, or "Pax Americana" as it was known (which wasn't "pax" at all given the millions violently killed in U.S. wars, which is the very reason why it was so short-lived... but that's besides the point).
But this transition is extra special, because for the first time in 300+ years, we have non-Western states such as China becoming preeminent powers. As we all know, ever since the Industrial Revolution, it was the West dominating the system. Transitions occurred but between Western states: Portugal to Spain, Spain to the British, the British to the US.
So that's the backdrop. Now how does Israel fit in and why does it matter?
Orders are based on principles, and founding historical events matter enormously to underwrite these principles.
Go back to the past, when the West started colonizing the planet, at first timidly (a few "trading posts" in Africa in the 15th century) and then more and more boldly, all the way to claiming entire continents. Why? Because they could, they were writing the principles (or lack thereof) of a new West-dominated world order.
Or if you want a closer example, take NATO's bombing of Yugoslavia in the 1990s, one of the founding acts of the US hegemony era. Completely illegal with regards to international law or even of NATO's own treaty (Serbia didn't attack and wasn't preparing to attack a member state of NATO), so much so that - it's funny to recall today - even Ariel Sharon at the time called an act of "brutal interventionism". Looking back, it premised the entire US hegemonic order: a time of unilateral, hubristic and brutal interventionism with little regard for international law. The message was "we do whatever the hell we want"... And this first act was timid compared with what was to come afterwards and the millions killed in the post 9-11 so-called "war on terror".
Now I'm obviously not suggesting that Israel will be a preeminent state in the new world order, it's way too small for this. What I am saying is that the actions we collectively permit today will echo for decades to come and define the larger battles that will shape our future.
And everyone can see that the precedents that we're setting are beyond horrifying: some of the principles Israel breaks were established for centuries such as the illegality of bombing embassies, or the killing of medical staff. Even in the Middle-Age we knew better not to do that stuff.
People don't realize just how consequential this is: what's at stake is quite simply everything. If we let the future of the international order be based on the murder of Palestinians, and now the Lebanese, we're paving the way for the most unprincipled and nihilistic order we've ever known, where virtually anything goes.
I see many people, some of them I believe sincere, defend Israel on the basis that it's a "fight for civilization against barbarism". It's in fact the EXACT CONTRARY. Israel is literally destroying everything civilization is based upon: sovereignty, the rule of law, human rights, freedom, etc. If you care about any of these things and if you truly understood what's happening, you'd be an ardent defender of the Palestinians and Lebanese.