Theory:

     By climbing the summit of Everest you are overwhelmed by a deep sense of joy and thankfulness. It is a joy which lasts a lifetime. The experience changes you completely. The man who has been to the mountains is never the same again.
 
     As I look back at life after climbing Everest I cannot help remarking about the other summit — the summit of the mind — no less formidable and no easier to climb.
 
     Even when getting down from the summit, once the physical exhaustion had gone, I began asking myself the question why I had climbed Everest. Why did the act of reaching the summit have such a hold on my imagination? It was already a thing of the past, something done yesterday. With every passing day, it would become more remote. And then what would remain? Would my memories fade slowly away?
Explanation:
 
According to the narrator, climbing to the summit of Everest filled people with a great sense of excitement and gratitude. It was a kind of thrill that lasts forever. He further stated that the experience gained from climbing the mountain would completely transform the people.
 
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Climbing to the summit fills a man with a deep sense of joy and thankfulness

A man who had climbed the mountains would not be the same again. The reason behind the statement is that if one attempted to climb Everest or any other mountains, they would reach their target after encountering numerous challenges. The difficulties or struggles they encountered along the way taught them a valuable lesson or motivated them to succeed in life. After finishing mountain climbing, they would face their lives with challenges. In addition, the narrator remarked that while climbing the mountains, one became aware of his insignificance and loneliness in this vast universe.

When he reflected on his life after climbing Mount Everest, he couldn't stop thinking of another big summit. Here another big summit implies one's mind, which wouldn't be much easier to climb. No one can give a complete answer to what one guesses or what one forecasts when it comes to our mind. The mind's thought goes beyond our imagination. The narrator mentioned that, like climbing Everest, it was not easier to climb on one's mind or thoughts. Climbing the summit within was more challenging as well as it was not easier to climb.

After returning from Everest and recovering from the physical tiredness, the narrator began to question himself why he had climbed the world's highest peak. It wasn't easy to understand why the achievement had such a long-lasting impact on his thoughts; it was a thing of the past that feels like it had done yesterday. With each passing day, he was well aware that the experience would get old. He wasn't sure if the memory would last or if it would go away gradually at the time.
 
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The narrator questioned himself as why he had climbed Mount Everest
 
Meanings of the difficult words:
 
S.No
Words
Meanings
1
Overwhelm To cause someone to feel sudden strong emotion
2
Exhaustion A state of extreme physical or mental fatigue or tiredness
3
Formidable Inspiring fear or respect through being impressively large, powerful, intense, or capable
4
ImaginationThe ability to form pictures or create something in mind
5
RemoteFar away in time or past
Reference:
National Council of Educational Research and Training (2008). Honeydew. The Summit Within- H P S Ahluwalia (pp.75-82). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.