Hezbollah has kidnapped the soldiers in order to negociate the release of the Lebanese prisoners in the Israeli Prisons. And even though many (but not all) of these Lebanese Prisoners were arrested inside the Lebanese Borders, they were were arrested in the region occupied by the Israeli army, there fore a region under the Israeli authority. In addition all of the Lebanese prisoners were Hezbollah actual fighting activists that had, or were planning, for some actions against the Israeli army. And to top that all, these prisoners were arrested at least 10 years ago, which puts serious doubts about Hezbollah's intentions.
Hezbollah is in fact forced to do this huge and useless stunt, simply because it has reached a point where things were inevitably degrading to the point where it would have to disarm. In spite of all the apparent strength of Hezbollah, it was plane obvious that they can't keep there weapons for ever. They had a few allies, its strongest ally and by far its only reason to exist was Aoun (I wouldn't possibly expand this to say that they had the LFPM's support, but they had at least Aoun's support); in addition they had there traditional ally and rival Amal (again that support was not absolute, and many clashes between Amal and Hezbollah's activists took place demonstrating the fragile union between the two); finally they had the President of the state, Emile Lahood, the latter’s support was meaningless since he had absolutely popular support at all, but alot of effort was put to depose him and the longer he remained the longer Hezbollah's weapon was not discussed.
But despite of all these, more or less, powerful allies, Hezbollah's time was running out.
They were under pressure from Aoun himself. There strong Maronite ally was clearly upset with Hezbollah's way of exploiting the LFPM's alliance. In every occasion in which the LFPM / Hezbollah / Amal / Marada / Karameh 's alliance would organise any sort of popular demonstration, all sort of Pro - Syrian slogans were raised. The LFPM, despite its alliance with the Pro-syrians would never accept Pro-Syrian slogans. In fact the Pro-Syrians had in fact apologised for Aoun because of there actions during the past 30 years and especially during the past 15 years. Aoun and his block did try to justify the Pro-Syrian actions of there allies in front of the Lebanese public opinion and especially in front of there supporters, but there are limits to everything and eventually Aoun was putting increased pressure on Hezbollah and the rest of there allies to behave. And in fact the LFPM publicly retreated from one of the public demonstration in Tripoli
- The National Dialogue did not achieve a lot, but it did achieve crucial points. At the moment when the escalation took place, the National Dialogue was Discussing the Hezbollah weapons' issue or as it is publicly known the common defense strategy and Hezbollah was very vulnerable. In fact Hezbollah had to give a commitment to never attack Israel, if they are to keep (temporarily) there weapons. And Hezbollah really needed to make its move before the commitment would be made public.
- Hezbollah was losing another ally, Amal. Not that Amal would ever dare to turn against its traditional ally/rival, but you see, the Hezbollah was going to be disarmed, sooner or later. Amal always hated the fac that Hezbollah would be armed, because that gave the latter the advantage against them, Berry (representing Amal) was the third president of the country but everybody knew that Hezbollah ruled with an Iron fist. Now in spite of this Amal chose to gamble on the Pro-Syrian camp, and there fore defend the Hezbollah weapon because they knew they would be weakened by the Syrian retreat. Again they chose to gamble and defend Hezbollah's right to own weapons, because they knew that the public Shiia opinion might reject them, as they will surely reject Hezbollah. But now things have changed, both the Syrian and the Hezbollah front are to be lost, and Amal has now the chance to appear as the moderate Shiite leadership, unlike Hezbollah they have more public support (if the terror factor of Hezbollah is put aside). And in fact, we have noticed recently increased moderation in Amal's opinions.
- Hezbollah, let's not forget this, were never Lebanese, even though they have all the prerequisites to become Lebanese, but they never wanted that. Hezbollah's clearly more Iranian than Lebanese and IF they ever choose to integrate the Lebanese society they will fail, they have relied for too long on there terrorising uniqueness and Iranian support. Now they are simply not part of Lebanon, the moment people will cease to fear them, the people will devour them. And at this moment the Iranian needs demand from Hezbollah to create a noisy situation, so they did.
For all these reasons, and probably for many others, Hezbollah chose to attack.