¿Qué significa She felt she 'had been entrusted with something as valuable, as telling and prophetic as a first love when the lover reads it, like an omen, for the future'. ?

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She felt she 'had been entrusted with something as valuable, as telling and prophetic as a first love when the lover reads it, like an omen, for the future.’

This statement is romantically and poetically exaggerated. References to ‘prophetic’ and ‘omen’, are to be taken lightly.

“She felt she..” = she thought / interpreted / believed
“..'had been entrusted with..” = given something by someone, to take care of / look after
“.. something as valuable” = something important or precious
“as telling and prophetic..” = revealing and like messages from a prophecy (something that is believed or predestined to be true)
“.. as a first love, when the lover reads it,” = *In context only: like a lover reading this (story) of their first love.
“like an omen, for the future.’” = like a sign of foretelling a prophecy, for the future (a hope like fate)

The author believes she was given something precious, a love story of a persons first love / romantic encounter. That story being told in the belief of romance and true love, hopeful and with pure feelings of the future.