sermon vs kerugma

sermon and kerugma both are nouns.

Word	Noun	Adjective	Verb	Adverb
sermon	Yes	No	No	No
kerugma	Yes	No	No	No

As nouns, kerugma is a hyponym of sermon; that is, kerugma is a word with a more specific, narrower meaning than sermon:

sermon: an address of a religious nature (usually delivered during a church service)
kerugma: preaching the gospel of Christ in the manner of the early church

Other hyponyms of sermon include baccalaureate, kerygma, evangelism, homily, preachment.

sermon (noun)	kerugma (noun)
an address of a religious nature (usually delivered during a church service)	preaching the gospel of Christ in the manner of the early church
a moralistic rebuke