Theory:

     And I saw that it was indeed himself but how aged and wan! And never before had I heard him mention his brother. Much shocked, I murmured, “Oh! I am sorry!”
 
     “Yes,” he answered, “he was a good man, he made a good bood. But he is dead.” And he touched the top of his head, where the hair had suddenly gone as thin as it had been on that of his poor brother, to indicate, I suppose, the cause of his death. “Do you wand any boods?” And he held up the leather in his hand. “ld’s a beaudiful biece.”
Explanation:
 
The author was taken aback when he learned of his elder brother's death. The loss of the elder Gessler grieved the author. The author mistook the younger Gessler to be the elder Gessler, and soon after their conversation, the author realised his misunderstanding because his appearance showed that he resembled his elder brother. The younger Gessler appeared exhausted and pale. The reason was obvious to the author. The Gessler brothers worked twenty - four hours a day, seven days a week, to retain the few clients.
 
And, when the author expressed his sincere sorrow for the eldest brother's death, the bootmaker responded, "he was a good man, he made a good bood. But he is dead.". The younger Gessler's statements expressed his affection for his older brother and how much he missed him. After all, the Gessler brothers worked around the clock to run the Gessler shop and supply high-quality products.

The Gessler brothers had no disagreements about profit or the quality of the boots they created. They worked together for quality rather than profit. People who knew the Gessler brothers would agree that they were the best bootmakers they had ever seen. The Gessler brothers were the greatest bootmakers anyone had ever seen, according to those who knew them. It's no wonder that the author was saddened by the loss of such a great man (the elder Gessler). Then the younger Gessler touched the top of his head, where his hair had suddenly thinned to the same extent as his unfortunate brother's as if to suggest the cause of his death. "Do you want any boots?" he then inquired of the author. He showed the author the beautiful piece of leather he was holding.

As previously stated, the Gessler brothers may have lost clients due to insufficient advertising, failure to fulfil client deadlines, and other factors. As a result, they must have continued to work hard without taking enough breaks to deliver boots in less time and keep their customers. As a result, the Gessler brother's death and younger Gessler's aged appearance were most likely caused by this.
 
Meaning of difficult words:
 
S.No
Words
Meaning
1.
WanLooking pale and weak
2.
RetainTo hold/keep someone or something 
3.
MurmurTo say something in a quiet voice
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.