Theory:

     She stretched out the first finger of her right hand so that it served as a perch and the little bird flew down and sat on it. Then, followed by her Maids of Honour, she went through the palace and called on each of the Princesses. And for each of them the little bird sang a different song. But the parrots could only say ‘God save the king’ and ‘Pretty Polly’. At last she showed the little bird to the King and the Queen. They were surprised and delighted.
 
     “I knew I was right to send you to bed without any supper,” said the Queen.

     “This bird sings much better than the parrots,” said the King.

     “I should have thought you got quite tired of hearing people say ‘God save the king’,” said the Queen. “I can’t think why those girls wanted to teach their parrots to say it too.”

     “The sentiment is admirable,” said the King, “and I never mind how often I hear it. But I do get tired of hearing those parrots say ‘Pretty Polly’.”
 
     “They say it in seven different languages,” said the Princesses.

     “I dare say they do,” said the King, “but it reminds me too much of my Councillors. They say the same thing in seven different ways and it never means anything in any way they say it.”
Explanation:
 
To depart to meet her eight sisters, the Princess extended out her right hand's first finger, which acted as a platform. The little bird crashed down and landed on it.
 
shutterstock_1753186301.jpg
A bird sitting on a finger like a perch
 
September marched briskly through the castle and summoned each of the Princesses. She made her pet bird entertain the other Princesses. Each of the eight Princesses received a distinct song from the bird.
 
On the other hand, the parrots could only utter 'God save the king' and 'Pretty Polly.'
 
Finally, she presented the King and Queen the tiny bird. They were both shocked and overjoyed.
 
The Queen was the one who spoke out first. She reflected on how she had made the correct decision to send September to bed without an evening meal. The King compared the bird to parrots. He stated that the songbird sang far superior to the parrots.
 
Because 'God save the king' is the most popular chant globally, the Queen assumed the King would become bored of hearing the parrots repeat it. The Queen was even surprised about why their daughters had chosen to teach their parrots that exact phrase.
 
Despite the parrots' and people's constant shouts of "God save the king," the King found the spirit commendable. However, he indicated that he had become bored of hearing the parrots exclaim 'Pretty Polly.'
 
The Princesses decided it was time to stand up for their parrots. As a result, they reminded their parents that the parrots could say "Pretty Polly" in seven different languages.
 
In turn, the king acknowledged the princesses. He said, jokingly, that the parrots reminded him too much of his counsellors. He believed that both sides might say the same thing in seven different ways, none of which would make sense.
 
We could analyse the King's and the Queen's characters well after presenting to them the nightingale. Until then, the parrots were celebrated by the couple. However, after the songbird's arrival, they heaped praises over the bird. The Queen went a step ahead in treating her careless attitude towards her children as right and just.
 
Despite being overtly connected with the parrots in the past, the King and the Queen found the parrots absurd after listening to September's pet bird. Also, without considering the eight Princesses' mindset, the King said he could tolerate "God save the king" as it demonstrated his reign over the kingdom. But, "Pretty Polly" did not excite him anymore.
 
The King and the Queen only cared about momentary needs, from naming the Princesses to shifting their fondness towards the songbird. The couple never bothered about the long run and the implications their words might have had on their children.
 
Meanings of difficult words from the paragraphs:
 
S.No
Words
Meanings
1
PerchAn edge of something
2
AdmirableDeserving respect or approval
3
I dare sayIt is a phrase used to emphasize one's strong opinion
Reference:
National Council of Educational Research and Training (2008). It so happened. Princess September - Somerset Maugham (pp. 34 - 44). Published at the Publication Division by the Secretary, National Council of Educational Research and Training, Sri Aurobindo Marg, New Delhi.