Theory:

     “Mr Gessler in?” I said.
 
     “No, sir,” he said. “No, but we can attend to anything with pleasure. We’ve taken the shop over.”
 
     “Yes. yes,” I said, “but Mr Gessler?”
 
     “Oh!” he answered, “dead.”
 
     “Dead! But I only received these boots from him last Wednesday week.
Explanation:
 
Gessler could no longer bear the shock, and he directly inquired the new labour (Englishman) in Gessler's shop about him (Gessler). The Englishman informed the author that Gessler was no longer available. He then went on to say that he was happy to help with anything and that he had taken over the shop.

However, the author did not listen to his comment and kept repeating his question as the author was confused and his mind was full of questions about Gessler. The Englishman recognised the author's worry for Gessler and replied that Gessler was no longer alive.

The author did not have expected such an answer from the stranger (Englishman); he was struck for a while. The author couldn't accept the stranger's (Englishman) words. He informed the man that he couldn't be dead because he had only gotten the boots last Wednesday. The author's mind did not accept the fact that his old friend was dead.
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.