mantra vs sacred writing

mantra and sacred writing both are nouns.

Word	Noun	Adjective	Verb	Adverb
mantra	Yes	No	No	No
sacred writing	Yes	No	No	No

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

mantra: (Sanskrit) literally a `sacred utterance' in Vedism; one of a collection of orally transmitted poetic hymns
sacred writing: writing that is venerated for the worship of a deity

Other hypernyms of mantra include religious text, religious writing, sacred text.

mantra (noun)	sacred writing (noun)
(Sanskrit) literally a `sacred utterance' in Vedism; one of a collection of orally transmitted poetic hymns	writing that is venerated for the worship of a deity
a commonly repeated word or phrase