Since water boils at 100°C (212°F), you cannot get the food any hotter than that without drying it out, unless you’re using a pressure cooker. So cooking food is a balance between overcooking the outside and undercooking the inside. Too high a heat and the outside burns before the interior has had a chance to heat up. Too low a heat and the length of time it takes dries out the exterior. For roasting or baking an average sized portion of food, 350°F is pretty near the optimum, with of course exceptions: a really big piece of meat like a turkey has to be cooked longer at a lower heat, usually around 325°F, and some things can take a higher heat for a shorter period of time.
A lot of things having to do with cooking are related to the basic necessity of heating the food long enough for the interior to cook without burning or drying out the exterior. You can use wet methods (boiling, simmering, crock pots, pressure cookers), you can cook thinly sliced or finely diced food (stir fry, etc.), or you can coat the food with something that shields it from direct heat and retains moisture (breading, basting, sauces, oven bags, etc.)