Well, they used that poem and quotes by the the Archpoet and from the Carmina Burana earlier in OUAT (Cora/Regina’s spellbook) and in Wonderland (The book in “Forget Me Not”).
Here they used mostly some other strophes of the “Vagabond confession” but it’s still the same poem.
So I think ther isn’t a big meaning behind it because it looks like they use it as a latin filler text for spellbooks or grimoires like they did it with “Snow White and Rose Red” and the “The golden Bird” for the Storybook.
About other stuff they use for this book.
Well, there definetevly some astronomical and alchemistic symbols and letters from an occult alphabet which looks very similar to three occult alphabets Heinrich Cornelius Agrippa published in the 16th century.
But still they used it also for the other two magical books.
“There were thousands and thousands of forms of joy in the world, but that all were essentially one and the same, namely, the joy of being able to love.”