It's said you can see the universe in a grain of sand, and that every human being is a microcosm of the universe.
In the same way, in every sentence of a language (and sometimes in just a single word), there are a number of lessons that you can extract which teach you about the language at large.
For example, the simple phrase in Brazilian Portuguese, 'Oi, tudo bem?' (Hi, everything well?), could be analyzed for its pronunciation/phonology, vocabulary, even seedlings of grammar with some imagination.
In fact, if you just say the name of a foreign language over and over again ('français, français, français', for example), it kind of sounds like you're speaking that language. In other words, it gives you a general, microcosmic representation of the language.
I think an eye for this kind of recursiveness - being able to see the proverbial forest by looking at one tree (or even just a leaf) - and the patience to do so, are among the most important skills to apply to language learning.