Alright, it is true that these sentences are quite unusual. When you talk about things you usually want to at least specify what things you are talking about or at least say the thing or the house and so on. We run into a problem here, though:
Swedish words for the are virtually the same as their words for a: en and et.
Well, you have a modification in that ett, as it becomes et, but you can't really here it very well in speech.
But this is confusing, right? If you want to say the thing, you can’t say en sak, because that would be the same as a thing. Luckily, Swedes figured out how to solve this confusion:
The Swedish words for the (en and et) go at the end of the word instead of in front of it.
Now that clears up the confusion. For example, if you have an et-word hus, you could say ett hus and that would mean a house, or you could put et at the end of the word and have huset to mean the house.