sacred text vs piece of writing

sacred text and piece of writing both are nouns.

Word	Noun	Adjective	Verb	Adverb
sacred text	Yes	No	No	No
piece of writing	Yes	No	No	No

As nouns, piece of writing is a hypernym of sacred text; that is, piece of writing is a word with a broader meaning than sacred text:

sacred text: writing that is venerated for the worship of a deity
piece of writing: the work of a writer; anything expressed in letters of the alphabet (especially when considered from the point of view of style and effect)

Other hypernyms of sacred text include writing, written material.

sacred text (noun)	piece of writing (noun)
writing that is venerated for the worship of a deity	the work of a writer; anything expressed in letters of the alphabet (especially when considered from the point of view of style and effect)