Theory:

     There is another summit. It is within yourself. It is in your own mind. Each man carries within himself his own mountain peak. He must climb it to reach to a fuller knowledge of himself. It is fearful, and unscalable. It cannot be climbed by anyone else. You yourself have to do it. The physical act of climbing to the summit of a mountain outside is akin to the act of climbing the mountain within. The effects of both the climbs are the same. Whether the mountain you climb is physical or emotional and spiritual, the climb will certainly change you. It teaches you much about the world and about yourself.

     I venture to think that my experience as an Everester has provided me with the inspiration to face life’s ordeals resolutely. Climbing the mountain was a worthwhile experience. The conquest of the internal summit is equally worthwhile. The internal summits are, perhaps, higher than Everest.
Explanation:
 
Then the narrator stated that the climb to Mount Everest changed him completely. It made him a different person. Apart from the physical summit, the narrator said that there was another summit, the summit within one's mind. He described how each person's mind had a mountain peak that must be climbed to achieve perfect awareness of oneself.

Later the narrator stated that the summit within was terrifying and unquantifiable. Furthermore, one had to climb on their summit. He explained how physically ascending a mountain was equivalent to climbing a mountain inside one's mind. The effects of both climbs are the same as well. Regardless of whether the ascent was physical, emotional, or spiritual, it utterly transformed everyone. It would teach a lot about oneself and the world around him.

The narrator thought that his time as an "Everester" had given him the strength and inspiration to face life's adversities with courage and determination. Climbing Everest was an unforgettable experience, and achieving the top within was no less so. Also, he stated that internal summits were higher than Everest's physical top.

Through this lesson, the narrator tried to tell his readers that, like mountain climbing, life has many hurdles. In everyone's life, there was a mountain peak. People should work hard to overcome the obstacles in their life. For that, the most important thing was one should realise their smallness in the vast universe. The narrator's wish was that everyone must climb the summit within oneself.
 
Meanings of the difficult words:
 
S.No
Words
Meanings
1
FearfulFeeling afraid; showing fear or anxiety
2
UnscalableNot able to be scaled or climbed
3
Venture A risky or daring journey or undertaking
4
Everester Someone who climbs Mount Everest
5
OrdealPainful experience
6
ResolutelyWith determination or firmness
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.