In America, we're not currently under any real threat of death for being a Christian. But that's certainly not true about our brothers and sisters throughout the ages and even today in many places around the world. Even still, whether we're really at risk of being killed for our faith or not, we're called to be faithful unto death. This is what the Savior said to the church in Smyrna.
After introducing Himself as "the first and the last, who died and came to life" in verse 8, Jesus says,
9 “‘I know your tribulation and your poverty (but you are rich) and the slander of those who say that they are Jews and are not, but are a synagogue of Satan. 10 Do not fear what you are about to suffer. Behold, the devil is about to throw some of you into prison, that you may be tested, and for ten days you will have tribulation. Be faithful unto death, and I will give you the crown of life. (Revelation 2:9-10)
Jesus was aware of the suffering they were going through. Not only did He know it, but He had planned it before all time for their good (Romans 8:28-30; Hebrews 2:10). But as a comfort to them, He reminds them that He knows their tribulation. Furthermore, He knows their "poverty." The text doesn't say how they had become impoverished, but it wasn't uncommon at the time for Christians to be marginalized in society, leading to material poverty. But Christ reminds them that even though they were poor, they were quite rich. They had Him and full access to His kingdom.
Not only had they been materially persecuted, but they were also slandered by those who said they were Jews but were not. This is probably speaking about those who claimed to be Jews but rejected Jesus, revealing themselves to not truly be Jewish. (See Romans 2:29; 9:6-7; 10:12.) Certainly, the Christian church endured much slander from the Jews who rejected Jesus Christ as the Messiah. Jesus goes on to strongly declare that such slanderers were not only false Jews but that they were "a synagogue of Satan." Far from being a synagogue of Yahweh, they were a synagogue of Satan.
With that background, Jesus tells the Christians in Smyrna to not fear what they were about to suffer. Their suffering was not going to let up; they'd continue in tribulation. But they did not need to fear. Why did they need not fear? We'll see that in a moment.
But in verse 10, Jesus continues to let them know that the devil was about to throw some of them into prison. Of course, it would be humans who would throw them into prison, but those humans would only be doing so in service to their god, the devil, even if they weren't aware of that. Spiritual warfare is real.
But God had greater purposes for the Christians' suffering. It was for their testing. It would strengthen their faith and show them to be true followers of Jesus Christ.
Jesus says that they would only have tribulation for ten days. Whether that's a literal ten days or not, we don't know--numbers are used symbolically throughout Revelation. But the idea is that--in the grand scheme of things--the suffering would only be for a little while.
Finally, He exhorts them to be faithful unto death, and He promises them a reward: the crown of life. This is probably not a literal crown but is rather speaking symbolically of their reward for their victory in Christ. They would be given eternal life.
Now, it's not because they earned it by themselves. Yes, they would have endured to the end, but they will look back and see that it was God Himself that strengthened and kept them the whole time (Philippians 1:6; John 10:28; John 3:16).
But focusing back on being faithful unto death, Jesus is calling them to faithfulness that would even welcome death if following Christ called for it. Not every Christian will die for Christ, but every Christian should be ready to do so, if necessary.
Are you? Even if you're in America or somewhere similar, do you recognize that following Jesus Christ might cost you your life one day? And are you ready for that?
Prepare yourself for that, Christian, by meditating on the word of God and being steadfast in prayer. Grow in your love and devotion for Christ daily, by His help, so that in the day of trouble, you will be able to endure suffering to the point of death. And if/when you do, He Himself will give you the crown of life.