In ancient times, France was called Gaul and the French were the Gauls (Gaulois). The rooster became the symbol of Gaul and the Gauls as a result of a pun. The Romans made fun of the Gauls, because, in Latin, the word Gallus means both rooster and Gaul. They regarded them as so boastful and noisy birds or roosters that were no match for the Roman eagle.
Thereafter, the kings of France will adopt the cock out of bravado. When meeting their rivals who treated them as roosters, they would say that the cock is a brave and early rising fighter.
The cock is also the bird of light and faith, the enemy of evil and darkness, etc….
There is a rooster on top of many churches in France. It is a very well liked symbol. I had a discussion with a priest yesterday at my nephew’s christening. He told me that wether a church had a rooster on top depended on a negotiation between the priest and the mayor of the village or town. Basically, since the separation of church and state in France, what tops the church (a rooster or a cross) pretty much depends on who pays the bills, the church or the village:)