Why Do We Get Wisdom Teeth?

The most likely answer is that they are vestigal bones -- they are left overs from a previous stage in human evolution.

Human ancestors millions of years ago had much bigger jaws than they do, today.  The jaw had to be bigger to cope with a mostly raw diet of vegetables; the only way we could get nutrition was through an awful lot of chewing, grinding our teeth down.  Not only did our teeth take more wear, but we needed more teeth full stop, to be able to eat enough.

Over time humans changed.  We mastered fire, and then cooking.  We became better hunters and cooking our prey made it easier to chew up.  Foreshortened jaws facilitated better quality speech, and humans that communicated better were more successful at breeding and surviving long enough to breed.   The extra teeth hung around, though, causing impaction and pain in many modern jaws that are simply too small for any extra molars.

Incidentally, the Creationist reply to all that is to say that somehow our modern diet of "soft" foods reshapes human jaws during childhood/growing up, and that's why wisdom teeth don't fit in most modern mouths.  Funny how they believe in physiological change over a few decades, but not over millenia!

We get wisdom to be knowing the right thing to do and be doing it