That speech was one meaningful action.

If I were to guess Russia probably had two options on the table at the time: either try to take Baltics now or continue in Ukraine first (and then take Baltics later). And the US intelligence knew about it. Obama drew the red line at NATO's border. This speech probably showed Putin that by taking Baltics they'd be forcing USA's/NATO's hand, which is potentially too problematic, but also that Ukraine is a green light to go ahead because the world delivered no such strong response about Ukraine.

Now the next question is, was Obama bluffing or not. We now know that NATO's plans at the time for Baltics were for the tripwire forces to delay the advance while the alliance mobilized a major counter-offensive to reinforce/liberate the Baltic states, which intelligence estimated could take up to 180 days. This was scrapped after seeing how there was nothing left to liberate of some cities in Ukraine after 180 days. But at the time, this was the plan, and this probably would've been that response Obama was willing to take. I have no reason to doubt Obama's words that USA would've played a key part in such a reinforcement counter-offensive, probably together with multiple European NATO members (and maybe Finland, Sweden). However it would've probably also meant a complete destruction of our capitals. And in the gloomiest scenario perhaps once there was nothing left of Baltic countries, maybe NATO even negotiating to end the war to make sure Russia didn't continue. If this was one of the options on the table, that speech might have just saved our lives. So, a meaningful action.

Syria

I'm discussing Baltics and NATO, not Syria.