The IRGC (Islamic Revolutionary Guard Corp) is the most important part of the military. It’s supposed to guard the revolution: put down any internal revolts or coups. But it’s also the primary arm involved in places like Syria and Lebanon.
Among the information coming out after the fall of Assad one of the most interesting bits was on internal tensions inside the IRGC. It seems that the younger members are far more radical than the older guys currently in charge of the Republic. Khameini changed recruiting to invite only and upped indoctrination to 50% of training time, and, well, it worked. The younger members are true believers. They wanted to go into Syria and save it. They want more military action against Israel and find the missile strikes inadequate and pathetic.