Apparently, Russia is selling a missile system to Syria that is capable of targeting just about the whole of Israeli territory. Haaretz - Israel News - Syria missile deal said at heart of Israeli-Russia crisis. Of course, Syria, being Syria, will only use this for self defense. And first strike is the best kind of defense.
The Russians would say that this is not political, and maybe it isn't. Could be they would be selling to Israel if Israel were buying; at least that is what they would say. The fact is that Russia still has clients in the area for Russian built weapons systems. And Russia has made it a matter of trade policy to sell weapons systems. So this is just a matter of business to them. And business is business; no offense meant.
There is another argument, however. For Russia as it is for other countries, it is ostensibly about business but it may really be about geopolitics more than it is about money. For one things, it is hard to believe that they would get enough to really make a difference in their balance of payments on any of these systems. A much bigger payoff would come from focusing on oil production and distribution. And John Ralston Saul, in his book, Voltaire's Bastards, argues quite convincingly that countries end up subsidizing their weapons sales in the end anyway, so the people of a given country are always footing the bill in any of these transactions. Point is that there is no net economic gain from these sales.
The fact is that it is a matter of pride for nations to sell weapon's systems. But more to the point, it is a way for a country to project force and influence around the world, that is probably pushing it. For Russia not to sell to Syria would be for them to give up power they have in the region. That they do not want to do. So deep down it is really about politics, not business.
For Israel though it is one more threat to its survival.