grace of God vs free grace

grace of God and free grace both are nouns.

Word	Noun	Adjective	Verb	Adverb
grace of God	Yes	No	No	No
free grace	Yes	No	No	No

As nouns, grace of God and free grace are synonyms defined as:

grace of God and free grace: (Christian theology) the free and unmerited favor or beneficence of God

Other synonyms of grace of God include grace.

grace of God (noun)	free grace (noun)
(Christian theology) the free and unmerited favor or beneficence of God	(Christian theology) the free and unmerited favor or beneficence of God