What does Revelation 2:10 mean?

Don’t be afraid of what you’re about to go through. Some of you will be thrown in jail to be tested, and you’ll have a hard time for ten days. Stay faithful, even if it costs you your life, and I’ll give you the crown of life. Revelation 2:10 - Modern Text Bible

(He warns them about coming persecution but encourages them to stay loyal, promising eternal life to those who endure.)