The writer of the book of Hebrews writes about insulting the Spirit of grace.
Hebrews 10:29 says:
"How much more severely do you think someone deserves to be punished who has trampled the Son of God underfoot, who has treated as an unholy thing the blood of the covenant that sanctified them, and who has insulted the Spirit of grace?"
What does it mean to insult the Spirit of grace?
Who insults the Spirit of grace?
To find the answers to these questions, we must understand the book of Hebrews.