Posturing and an act of intimidation is the only motive at this point for Russia to send a warship into the eastern Mediterranean between Syria and US destroyers that fired Tomahawk missiles last night. Putin is an ally of Assad because Russia has interest in Syria's seaport as well as a gas pipeline.
The Russians couldn't careless about Syrian civilians getting wiped out by chemical weapons. Weapons that Syria is not suppose to have, that were supposed to have been turned over to Russia! (Thank you for lying they were Susan Rice and John Kerry). If Assad is removed from power, which Sec Tillerson has made clear, Russia's interests will be in question. It would be in Putin's best interest to join the civilized world to see Assad removed from power, replaced with someone who will uphold their interests but also bring an end to this civil war.
Instead, Putin chooses to puff his chest that will lead to a standoff in the Med as Russia has apparently disconnected the "deconfliction" line with the US. Now our troops on the ground will have no warning of impending Russian military activity. Do not be surprised to hear about "friendly fire" incident between the US and Russia. This is Putin's way of testing Pres Trump, who should pull out troops out of Syria immediately if this line remains disconnected.
If you're wondering or are still in doubt, after people like Mark Levin have issued warnings, yes we are in the early stages of WWIII!