Gemayel was a Maronite (Eastern Rite Catholic, majority of all Christians in Lebanon) and leader of the anti-Syria bloc. The Gemayel family is a dynasty in Lebanon. The grandfather help found the Phalangist Party and a son of the senior Gemayel was assassinated when he was president-elect. The last time a Gemayel was assassinated the Lebanese broke out in full force.
This attack plays into the Hezbollah/Syria/Iran axis (and they are the one's who most likely did it). Hezbollah removed its supporters from the government last week. With this assassination only two more ministers must resign or be killed to have the government constitutionally collapse.
Hopefully there will be another massive Cedar Revolution and it will be able to convince the international community to disarm Hezbollah and punish Syria and Iran. However, I do not foresee that happening. Expect more fighting.