Hezbollah’s distracting and costly engagement in the Syrian civil war has offered some practical benefit to Israelis. It has also been a source of foreboding.

On the one hand, Hezbollah, the militant Lebanese Shiite organization that fought a monthlong war against Israel in 2006, is preoccupied with shoring up the government of President Bashar al-Assad of Syria in its struggle against rebel forces, and is suffering losses.

But Hezbollah is also acquiring battlefield experience, and the only way for Mr. Assad, a longtime Hezbollah ally, to repay the group is by supplying it with sophisticated weapons, according to Israeli military officials and experts — strengths that could eventually be used against Israel.