AdverbIN BRIEF: That's a standard construction for comparatives: the ... the ...
1. With a comparative or more and a verb phrase, establishes a parallel with one or more other such comparatives.
2. With a comparative, and often with for it, indicates a result more like said comparative. This can be negated with none.
- The hotter, the better.
- The more I think about it, the weaker it looks.
- The more money donated, the more books purchased and the more happy children.
- It looks weaker and weaker, the more I think about it.
- It was a difficult time, but I’m the wiser for it.
- It was a difficult time, and I’m none the wiser for it.
- I'm much the wiser for having had a difficult time like that.
Each 'the' is followed by a comparative. That example above is the simplest formation and would refer back to something previously said, so many of the words are simply understood. For example, if someone had offered you a piece of cake and wanted to know whether you wanted a big piece or a small piece, you might answer "The bigger (the piece of cake is) the better (I will like it)."
you will also find more complex the... the... sentences:
The longer you wait, the worse it will get.
The more fruit you eat, the healthier you will be.
The less time you waste, the better off you will be.