Theory:

A thing of beauty is a joy for ever:
Its loveliness increases; it will never
Pass into nothingness; but still will keep
A bower quiet for us, and a sleep
Full of sweet dreams, and health, and quiet breathing.
Therefore, on every morrow, are we wreathing
A flowery band to bind us to the earth,
Spite of despondence, of the inhuman dearth
Of noble natures, of the gloomy days,
Of all the unhealthy and o'er-darkened ways
Made for our searching: yes, in spite of all,

Some shape of beauty moves away the pall
Explanation:
  
There is beauty in all the things we see around us. It brings us happiness when we see something beautiful. Its attractive beauty always increases, and it can never end. Even as it ages the beauty increases, and it can never stop - it is permanent and keeps growing. Beauty is eternal; it does not fade away.
 
beuaty.jpg
There is an ever-increasing beauty in everything around us!
 
The poet lists several beautiful objects around him. A bower refers to a pleasant shade under the trees. The beauty around us provides a calmlovely shade for us to relax, have a peaceful sleep filled with happy dreams; thereby leading us to have good health and soft rhythmic breathing. Beauty can be a healing therapy, which gives us a healthy body, mind and soul.
 
bower.jpg
Relax in a bower, enjoy the beauty!
  
Beauty enables us to cover ourselves in a band made of flowers, (a wreathe) to help us form a bond with the earth, every day. Our relationship with this earth can be wrapped like flowers in a wreathe if we enjoy the beauty around us.
 
wreath.jpg
A flower wreath!
 
Our earth is filled with evils/obstructions like:
  • sorrow, hopelessness
  • cruelty
  • absence of good-natured righteous people
  • sad and dark days
  • harmful and depressed system of life
Note that the word "spite" can be understood in two different ways:
  1. Instead of "in spite" (poetically)
  2. Intention to deliberately hurt someone
gloomy.jpg
Our earth is filled with despondence, inhuman nature, gloomy days and unhealthy ways of life!
  
But the poet says, we have to keep searching for beauty, which can make our life brighter despite all the evils around us. Some form of beauty can remove the (pall) cloth covering from all these problems. A pall can also refer to a dark cloud of smoke and dust. The poet compares our problems to this dark cloud, which can be removed by the beauty around us.
 
pall12.jpg
Problems engulf us like a dark cloud of some and dust!
  
Meanings of difficult words:
  
No.
Words
Meanings
1
nothingness
the absence or cessation of life or existence
2
bowera pleasant shady place under trees
3
morrowthe following day
4
wreathingform a circular band of flowers
5
spite
1. poetic form of "in spite".
2. a desire to hurt someone.
6
despondencein low spirits from loss of hope or courage
7
inhumanlacking human qualities of compassion and mercy
8
deartha scarcity or lack of something
9
gloomydark or poorly lit
10
pall
1. a cloth spread over a coffin.
2. a dark cloud of smoke, dust.
Reference:
State Council of Educational Research and Training (2019). Term-2 English Standard-8. A thing of beauty - John Keats (pp. 127-130). Published by the Tamil Nadu Textbook and Educational Services Corporation.