How would Russia be a military threat against Sweden if it joined NATO?

Factual Questions
1

According to this recent news story Russian spokespersons have said ““It’s obvious that if Finland and Sweden join NATO, which is first of all a military organization, it will entail serious military-political consequences, which would require retaliatory steps by the Russian Federation”

Now Finland is understandable since they share a massive border with Russia and they were previously part of Russia, but why the threat against Sweden? What military threat would Russia pose to Sweden if Sweden joined NATO? Sweden is bordered by NATO countries (besides Finland) so if Sweden by itself joined NATO it would be almost impossible to reach Sweden without overflying a bunch of other countries. In order to pull a Ukraine (which the implication is) they would have to march through either Finland or Norway to get to it, and there’s quite a bit of frozen tundra between the two countries, not to mention the fact both those countries have their own defenses.

2

Technically, they could launch out of St Petersburg or go the long way around from the Arctic but, yeah, it’s just saber rattling I think. No one seems to be paying attention to it.

(I’m ignoring Kaliningrad because I should)

Though, they do say “political consequences”. Maybe they included that one because of the logistical issues for military consequences.

3

If Sweden and Finland joins NATO then St Pete is surrounded on three sides and Murmansk get threatened.

Military response would likely entail a land based offensive into Finland to push the Finn’s away from their Baltic coast.

St Petersburg was literally built to defend against Swedish threats in the Baltic region, an interesting historical footnote.

4

Submarines. There is a history.