Answer:
The Valentine's name
Step-by-step explanation:
"Of poets, by poets—as the name is a poet's, too,
Its letters, although naturally lying
Like the knight Pinto—Mendez Ferdinando—"
"Search narrowly the lines!—they hold a treasure
Divine—a talisman—an amulet
That must be worn at heart. Search well the measure—
The words—the syllables"
They refer to the key of the riddle, which is the writers name.