The key word is a plural noun that gives the basis of the main points of the sermon. Read through the passage repeatedly while trying a selection of key words until you have what is sometimes called the "eureka moment".
Example
Passage: Romans 5:1-14
Subject: Suffering
Theme: Joy in suffering
Proposition: Every believer should rejoice in suffering.
Objective Sentence: Therefore every believer should rejoice in suffering.
Interrogation Sentence: Why should every believer rejoice in suffering?
Key Word: Results
Key Word
Preaching Tips
Key Word: Plural Noun