Why was Vivaldi referred to as 'Il Prete Rosso'?

Vivaldi was referred to as 'Il Prete Rosso', which translates to 'The Red Priest', primarily because of his distinctive red hair and his status as an ordained priest. His moniker reflects both his physical appearance and his clerical identity, linking his personal characteristics with his profession. While he was indeed involved in church music and served in a priestly capacity, the nickname specifically emphasizes the notable aspect of his red hair. This nickname has persisted throughout history as a fascinating detail about the composer, marking his unique identity in the world of classical music.

In contrast to the other choices, while he was prominent in Venice and did create church-related music, these elements are not the focus of the nickname itself. Vivaldi's musical style may have been peculiar or distinctive, but that characteristic does not contribute to the reason behind 'Il Prete Rosso'. Thus, the correct choice encapsulates both a physical characteristic and a personal attribute linked to his identity as a priest.