The Flood was more than an epic event.  It communicated key messages in God's Plan of Salvation for a world without sin.  

Key elements identified 

1. A world coming to a dead end 1almost 1700 years after creation of man.

2. Fixing the blame. Christ preached to the demons

3. The need to start again. God's Way will prevail

4. Repentance 

5. Salvation

A great resource to understand I Peter 3:19-21 is a sermon by Mitchell Knapp

htt1ps://www.ucg.org/sermons/christ-preached-to-the-spirits-in-prison