Wort Chilling Question

Long time lurker here, what an amazing resource!

I am on my 3rd batch, so far so good. I know from reading that the wort needs to be chilled to 70 as quickly as possible after the boil, but I was wondering why? What does this accomplish?

Thanks!

which part of it?

Why it needs to be quick or why you need to cool it? Ill take a shot at both...

The reason why doing so quickly is good is to reduce the time that it is exposed to the air (in the pot) so that you dont get any bacteria or infections from airborne stuff.

The reason why you must cool it to begin with is that you need to pitch the yeast when it is below 75 degrees. I have pitched at 80 and was okay but there is a chance that you can kill the yeast if it is too high.

chilling it quickly will help with cold break which will help with clear beer.

thanks guys, makes sense!