Why is it important for the body to maintain pH within a certain range?
The body has ways of always maintaining an optimal pH one of which are buffer systems which resist drastic changes in pH inside the body. A sudden shift in the pH of the body outside the normal range could prove detrimental.
One major effect of a shift of pH outside the normal range is the denaturation of proteins (particularly enzymes) which are paramount for the metabolism, growth and function of an organism. Enzymes has specific optimum pH ranges on which they are able to function. To acidic or too basic prevent these proteins to catalyze metabolic processes that could lead to sickness or death.