I'm knowingly ignorant of international politics. Can someone who follows this speculate the meaning of this?
The political side is that Sweden is not in NATO, as the electorate sees NATO as too global and too likely to draw the country into remote conflicts or the next world war. Russia is the only remotely plausible military threat in the region, so it's the bogeyman NATO will have to use if it wants to lure Sweden in. This incident will be used to argue the Swedish military is inadequate on its own. On the other hand Russia is testing everyone's military capabilities, e.g. Russian planes routinely skirt US airspace. In the 80's Sweden had lots of similar incidents (as well as confirmed ones: http://en.wikipedia.org/wiki/Swedish_submarine_incidents), and those didn't drive Sweden to join NATO. However Swedish society has become a lot less militant since then, abolishing conscription and reducing military budgets, and the memory of Sweden faring splendidly through WWII by staying independent is not as fresh. Eventually Sweden may end up in NATO solely because there isn't political will to do anything else.
If Sweden were to join NATO that could have implications for the neighboring Finland, which isn't in NATO either but still has conscription. Finland is the buffer between Sweden and Russia, so it is a given Finland would have an independent Sweden's backing.
Another thing is that there's much trade between Finland and Russia, and it's certainly old hat in Finland to fish for benefits by being the one European country that's not overtly russophobic. Finland even has much Russian military equipment.
Also, this video: http://www.youtube.com/watch?v=B19kYo80yec , though I don't really remember its backstory. (The RT article linked in the description seems to be reporting on a Swedish site reporting on that video, and the link to the Swedish site is broken.) But the impression I have got is that Russian media is overall unashamed in reporting on Russian interests abroad.
http://www.theguardian.com/commentisfree/2014/oct/20/guardia...
This is probably just a PR effort to sway the swedish public towards NATO partnership/affiliation. Perhaps there was no submarine, or it was a NATO one ...
Always ask yourselves: cui bono? The Russians have nothing to gain from risking a submarine in swedish (of all) waters. Sweden as a NATO member would be extremely useful to NATO at this point.
There is plenty of evidence that Russia is actively testing the military readiness of countries close to their borders. For example, intrusions by Russian military airplanes into Finnish airspace have increased tenfold compared to previous years.
Dismissing the submarine reports as a NATO ploy looks like a conspiracy theory when it's clear that Russia is actively doing this stuff all over their European border.
The entire idea of "objective gain" (and "Russia" as a unit that could have gain) is sometimes-useful but often misleading convenient fiction. All gain (in the sense that it motivates action) is grounded in subjective utility, and so is not objective, and, further, is the gain of individual actors for which larger entities (e.g., states) are potentially-misleading aggregate units of analysis.
Its not a matter of whether Russia has something objectively to gain from short military incursion, but whether Russian decision-makers feel that they have subjective utility tied to decisions which produce such incursions.
Testing detection and response capabilities, wiretapping undersea cables... they've been caught red handed in Swedish waters in the past.