I think the lion represents the principal of legitimacy.
The rose: the queen of flowers
It’s evident that the lion is among animals what the rose is among flowers. The rose is naturally queen. Put a truly beautiful rose among any other type of flower – even among a bunch of extremely beautiful orchids... the rose overshadows all other flowers, even the orchid. The rose is clearly superior.
The lion: king of the animals
Put a lion among every other animals... they are eclipsed.
The elephant is bigger, but…what a brute, vile mass. The camel walks further, but its step is like a heavy laden slave, it doesn’t break out with the proud step of the lion.
The lion marches and jumps, the camel walks.
Consider the fox: it is clever, but fragile; when his wit runs out, it is in trouble.
Consider the other animals: they all have some eminent quality, but none have the ensemble of qualities that make a lion a lion.
Look at the lion – it is king.
It seems to enjoy the right to be king: he commands, he has the claws of a king, he reigns!
It is normal that the lion be the color of a king. Gold is the color of kings. A silver lion – how frustrating! A golden lion, how natural!