Syria is under a dangerous and unstable minority regime, which needs to attack Israel in order to secure legitimacy. Currently, Syria could not attack Israel directly, so it uses proxies, like Hizbullah. The apparent weakness of the Syrian military is a ruse, though, as Syria is steadily rearming with Russian, Chinese, and Iranian armaments. It's air defense is already sophisticated. The most important interest for Syria is a powerful, preferably nuclear, Iran. If Syria had the Iranian nuclear umbrella, it would lose all inhibitions it ever had about attacking Israel directly. Let's not forget, shall we, that when in 1941 Finland had the backing of its ally Nazi Germany, it no longer feared the military might of the Soviet Union. In sync with the German Operation Barbarossa, little Finland attacked the mighty USSR.
U.S. says working on initiative to de-escalate Syria fighting, with focus on Aleppo (Reuters)
from the article: Israel sends conciliatory messages to Damascus