what is the importance of pepsin and hydrochloric acid in the digestion of protein?

Pepsin is secreted in
an inactive form, called
pepsinogen by chief
cells.

Parietal cells secrete
hydrochloric acid
which converts
pepsinogen to the
active pepsin only
when both reach the
lumen of the stomach,
minimizing self digestion

Minimize self digestion and pepsin hydrolyses proteins

the role of HCl is to break down large globs of protein. Relative to the digestive enzymes of the stomach, the normal size of a glob of food that enters the stomach is extremely large. So large in fact, that if something didn't break it down first, hardly any digestion would occur in the stomach at all.

Thus the role of HCl is primarily to create smaller, more managable particles of protein for pepsin to work with. It is a secondary, although vital, role of HCl to activate pepsin

Pepsin is a protease enzyme in the stomach, that breaks down proteins into polypeptide fragments and aminoacids.

Both HCl and Pepsin acts on proteins

HCl -            Protein mass------> managable small pieces
Pepsin-        Protein----------------> polypeptides and aminoacids