After being demilitarized in 2005, Sweden re-introduced permanent troops to Gotland in 2016, following Russia’s annexation of Ukraine’s Crimean Peninsula in 2014. Sweden also became NATO’s newest member in March — meaning it is covered by the alliance’s Article 5 guarantee that all other members come to each other’s defense if they are attacked.
What he is saying is that Gotland is extremely strategically important to Russia(and Sweden/NATO). It is also an island with 50k population, basically deserted, which can be used as an excuse(would countries be willing to go to WW3 over such an island?). An island that Sweden demilitarised in the past.
If Russia wants to fuck with the Baltic States(high probability, especially if things go well for them in Ukraine), Gotland will be part of that plan. Russia wants to deploy anti-air missile systems there that would enable them to air blockade the Baltic States.
This messaging is essential in order to signal to the world that a threat exists so if shit goes down, the world(NATO allies) will be mentally prepared to be involved.
It is “very easy” for Russia(or many countries who dont care about diplomatic fallout) to create a fait accompli and conquer small stuff. And then it is up to the morale of your country and your allies, to see if they have the will to fight back, like Ukraine did for example.