Hey guys, I have a quick question about the melodic minor scale. I know the descending form is used for the key signature, but I have no idea why the ascending form sharpens the sixth and seventh degrees. Can anyone help me?
My stuff

Gibson Les Paul Studio
Ibanez ADC120
Tanglewood TGRF VS
Blackstar HT20
Roland Micro Cube
The 7th is raised to allow for a perfect cadence in minor keys. The 6th is raised when approaching the cadence to avoid the augmented 2nd between the b6 and 7th degrees.

Harmonizing melodic minor also gives you more harmonic possibilities over using just harmonic minor.