Why a gold and a silver key on the Vatican flag?

Saint Anthony Mary Claret published a book called The Golden Key to Heaven, which sounds like two forms of salvation.

en.wikipedia.org/wiki/Flag_of_Vatican_City

the two keys which represent the Keys of Heaven (according to the Gospel of Matthew 16:19) given by Jesus Christ to St. Peter. The popes are regarded as the successor of Peter, and the gold and silver keys have been significant elements in the symbolism of the Holy See since the 13th century. The gold represents spiritual power, while the silver key represents worldly power. The order of the keys on the coat of arms of Vatican City is the reverse of the coat of arms of the Holy See, in order to distinguish between the two entities.

very interesting…

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