The missles in Syria wouldn't have an effect if there will be a large scale operation against this country. On the other hand with Russian Navy base there it would be a surprise if Putin leave its ally bare handed against annoying intelligence flights. Low cost and very efficient way to say that Russia finally cares. Bravo Putin!
Rohani: Nuclear deal achieves Iran's goals (AP)
from the article: Sharon: Russian missiles being sold to Syria do threaten Israel