Emperor Akbar and Birbal: Your king is the full moon

Emperor Akbar once ruled over India . He was a wise and intelligent ruler; and he had in his court the Nine Gems, his nine advisors, who were each known for a particular skill. One of these Gems was Birbal, known for his wit and wisdom. The story below is one of the examples of his wit. Do you have it in you to find the answer?
Once, Birbal was invited to Persia by the Persian king. He was honoured with celebrations in his honour and many presents and gifts were heaped on him.
After a few days of revelry and enjoyment, it was time to head back home. On the eve of his departure, a nobleman of Persia asked him how he would describe the king of Persia in comparison to his own king.
"Your king is the full moon," said Birbal. "Whereas mine is like the quarter moon."
The Persians were very happy with this answer and sent Birbal off with great pomp and gaiety.
But when Birbal got home, he found that Emperor Akbar was furious. It was obvious that information about his "praise" of the Persian king had preceded his own arrival.
"How could you belittle your own king?" demanded a furious Emperor Akbar. "You are a traitor!"
Birbal objected to this and said that he had. in fact, praised his own king! How did Birbal explain this to the king?

Answer
"No, Your Majesty," said Birbal. "I did not belittle you. The full moon diminishes and ultimately disappears whereas the quarter moon grows from strength to strength. What I, in fact, proclaimed to the world is that your power is growing from day to day whereas that of the king of Persia is declining."
Akbar was overjoyed at this answer and welcomed Birbal back with a royal embrace and a celebration in his honour.