Theory:

     Once (once only) I went absent-mindedly into his shop in a pair of boots bought in an emergency at some large firm. He took my order without showing me any leather and I could feel his eyes penetrating the inferior covering of my foot. At last he said, “Dose are nod my boods.”
 
     The tone was not one of anger, nor of sorrow, not even of contempt, but there was in it something quiet that froze the blood. He put his hand down and pressed a finger on the place where the left boot was not quite comfortable.
Explanation:
 
From the time the author was a child, he wore boots made by Gessler's siblings. In an emergency, the author once purchased a pair of boots from a large firm. And, the author walked into Gessler's shop with such boots, quite absent-mindedly.
 
When the author placed the order, the bootmaker took his order without showing him the leather material as he was busy observing the boots the author was wearing. The author could feel his (bootmaker's) stare piercing his foot's inferior covering. It's possible that the bootmaker was upset because he'd spotted the author wearing boots he'd bought elsewhere. The author, after all, was a regular customer. And the bootmaker produced a higher-quality product than he was paid for. "Those are not my boots," the bootmaker told the author after examining his boots for a time.
 
Following such remarks, the author felt depressed. Despite the fact that his voice was not one of anger, sadness, or even disrespect, the author was scared by his emotionless tone. He put his hand on the painful area of his left boot and pushed a finger against it. Because the bootmaker was an expert in the profession, he knew how to assess the quality of a boot. As a result, he was able to pinpoint the specific spot in the boot where it was uncomfortable.
 
Meaning of difficult words:
 
S.No
Words
Meaning
1.
Absent-mindedBeing lost in one's thoughts and inattentive to one's surroundings
2.
Penetrate/pierceTo pass into or through 
3.
ExamineCheck out carefully
4.
ContemptLack of respect
Reference:
National Council of Educational Research and Training (2007). Honeycomb. Quality - John Galsworthy (pp. 71-78). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.