Book of Joel vs Joel

Book of Joel and Joel both are nouns.

Word	Noun	Adjective	Verb	Adverb
Book of Joel	Yes	No	No	No
Joel	Yes	No	No	No

As nouns, Book of Joel and Joel are synonyms defined as:

Book of Joel (noun)	Joel (noun)
an Old Testament book telling Joel's prophecies	an Old Testament book telling Joel's prophecies
	a Hebrew minor prophet, the second of the twelve minor prophets