Can't I Just Heat On The Hob Or Microwave?
No, you can't.
If you used a hob the direct heat would be too strong and destructive.
If you used a microwave you would overheat the ingredient, at best; at worst, you would have some kind of an explosion.
Pyrex dishes won't crack from the constant heating and cooling.
If you choose to use another type of glass, i.e. not pyrex bowls or jugs, Make sure whatever glass bowl you are using can take the heat!
Have you ever poured boiling hot water into a glass tumbler - it cracked didn't it? That's what most glasses will do, pyrex is specifically designed to take heat well.