Hassan Nasrallah's speech has made it clear that Hizbollah is willing to sacrifice the safety of the Lebanese in defence of the slaughterer of Syrians.
Nasrallah lays bare the naked sectarianism of Hizbollah
For years, Hizbollah has carefully cultivated an image as a militia for all Lebanese, an iron wall that prevented further Israeli incursions in Lebanon. Even if the party/militia drew its most fervent support - and fighters - predominantly from Lebanon's Shia community, the group was always careful to portray itself as "Lebanon's shield". Even as Hizbollah's militia exerted increasing power across Beirut and increasing political power in the parliament, Hizbollah maintained the line that it was first and foremost for Lebanon.
No more. The speech by Hassan Nasrallah at the weekend pledging to stand by Bashar Al Assad has laid bare the naked sectarianism of Hizbollah, and shown that the group is willing to sacrifice the safety of the Lebanese in defence of the slaughterer of Syrians.
It's no surprise that Mr Nasrallah chose Saturday for his speech. For many Lebanese, even those who don't normally support Hizbollah, that day is marked as a reminder of the day, in 2000, when Hizbollah finally pushed Israel's military out of southern Lebanon. Indeed, in his speech, Nasrallah went out of his way to link the conflict in Syria to the two pillars on which Hizbollah has founded its legitimacy among non-Shias: defence of Lebanon (the "resistance", as Mr Nasrallah called it) and Palestine. "If Syria falls, Palestine will be lost," he said.
But those slogans are defunct. Hamas long ago abandoned the Syrian regime, rightly appalled at the way it has attacked civilians. Some have pointed out, both in sorrow and in anger, that Hizbollah has now turned its guns on other Arabs - as if the ethnicity of the enemy mattered, as if the Israeli-Palestinian conflict was in any way an ethnic conflict. In reality, what is most shocking is who Hizbollah has decided to stand beside.
The conflict in Syria is not, as Mr Nasrallah put it, between the Assad regime and "America, Israel and the takfiris". It is between Mr Al Assad and his own people. That militant jihadis have entered the fight against the Assad regime in no way changes the fact that the uprising began peacefully and only morphed into armed resistance once Mr Al Assad began slaughtering civilians. It is due to the inaction of the West, the indifference of the world and the infighting of the Syrian political opposition that jihadis were able to gain a foothold.
Despite the urgency and the moral tone with which the West has lamented the slaughter, the swift laying on of words of condolence for murdered Syrians, for those who have fled, for those who have died on the brutal battlefield that is now the entire country, or in refugee camps far from home, help has not been forthcoming to those still fighting for their homeland.
And yet the entry of Hizbollah does, however, unfortunately, change the likelihood of intervention and indeed of the likely composition of any future Syrian government. The open entry of Hizbollah into the conflict makes direct military intervention - already a distant prospect - almost impossible to imagine. The West, especially the United States, has long been nervous of even a solely air-led campaign, worried at how even one downed fighter jet would play with domestic opinion. A campaign against Hizbollah would be even tougher for the West: the Assad regime is no pushover, but the military prowess and reach of Hizbollah is formidable. Indeed, if intervention ever started to look likely, expect Mr Nasrallah to remind the West that it was 30 years ago this year that a small militia in Lebanon inflicted, in the bombing of the Beirut Marine barracks, what remains the worst attack on America's military since the Second World War.
For Hizbollah, the repercussions of siding with Mr Al Assad will be enormous. It places the group firmly in the Iranian camp. In the 20 years that Mr Nasrallah has led Hizbollah, he has gained a reputation among his supporters, and even further afield - "charismatic" being the adjective of choice for western publications writing about him - as a master strategist.
But this is surely a misstep. As much as many Arabs will find Hizbollah's decision a betrayal, the decision to stand by Mr Al Assad makes sense from a strategic point of view for the group - but only in the short-term. For Hizbollah, Assad's Syria is an important link in a chain that stretches to Tehran. But in the long-term, Hizbollah can only survive if large numbers of Lebanese support it, even tacitly. The Levant is too crowded a neighbourhood and legitimacy matters, even to the men with arms.
By siding with Mr Al Assad, Hizbollah has abandoned even the pretence of being a shield for Lebanon; it is now merely the arm of Iran.
In his televised address at the weekend, Mr Nasrallah warned that the end of Mr Al Assad would plunge the region into a "dark period". In fact, by so openly siding with a dying and discredited regime, by so openly siding with narrow political interests, and by allowing even the perception of naked sectarianism in a region of fragile alliances, it is Hizbollah that has all but guaranteed the coming of a wave of sectarian attacks, of which the attack on a Shia suburb in Beirut will be, tragically but inevitably, merely the opening salvo. Again and again voices from the region have warned of a coming conflagration; again and again, they have warned that if the fire in Syria was not swiftly extinguished, it would ignite the whole region. Now those predictions are coming true.
On Twitter: @FaisalAlYafai