Final answer:
The musician, represented by the Nightingale in the provided text, is the character who shows self-professed authority on love, offering its life to create a red rose symbolizing love's power.
Step-by-step explanation:
In the provided text, the Nightingale is the musician who believes in the transformative power of love and sacrifices itself to create a red rose for the sake of true love, demonstrating its authority on the subject. The dedication of the Nightingale to the ideal of love, and its belief in love's superiority over philosophy and power, portrays the musician as someone with a deep understanding and authority on love.
This example from literature illustrates how musicians, often through their art, express powerful emotions and ideas about love, arguably granting them a unique insight or authority on the subject.