Question

What does the hydrochloric acid not effect the cells lining the stomach

Answer 1

First, the mucosa doesn't get digested as it secretes the HCl because the pH within the parietal cells remains near neutrality

Second, HCl in the lumen doesnt digest the mucosa because goblet cells in the mucosa secrete large quantities of protective mucus that line the mucosal surface. Basic electrolytes, such as HCO3-, trapped inside the layer of mucus neutralize any HCl that penetrates the mucus.

This mucus layer also protects the mucosa from digestive enzymes in the lumen, but why dont the enzymes do damage before they are secreted from the exocrine cells of the mucosa? Because they are never present within the cells! The cells synthesize and secrete proenzymes that are larger than the active enzymes. Once in the lumen of the stomach, these proenzymes become active enzymes only by having part of the proenzyme molecule digested away, leaving the "business" part of the molecule to function.

Answer 2

Although hcl is secreted for digestion of proteins in stomach but the inner lining is not affected because of secretion of mucus which protects the inner lining of the stomach.
Hope that helps you :-)