The only place where “lily of the valley” occurs in the Bible is in Song of Solomon 2:1:
I am a rose of Sharon,
a lily of the valleys.
Here, Solomon’s lover is using a beautiful flower as a metaphor for herself. Solomon takes up the metaphor in response:
As a lily among brambles,
so is my love among the young women. (Song 2:2)
The Song of Solomon is a beautiful love poem that draws on many agricultural and botanical metaphors in describing the passionate love between Solomon and his lover.
Many commentators have considered the Song of Solomon to be an allegory of the love between Christ and his faithful believers, but this is not the primary meaning of the book.