Why do believers suffer imprisonment and tribulation according to Revelation 2:10?

Les explains that the church of Smyrna was going through horrible pressure. Their tribulation and poverty were material—persecution took away income, jobs, and wealth—yet spiritually they were rich. In verse 10, they are told to fear none of the things they would suffer, because the devil would cast some of them into prison for their faith, that they may be tried or tested, and they would have tribulation ten days. Les sees the ten days as ten distinct periods of time during the Roman Empire when the church came under horrible pressure. These believers did not give up; they went through it because the Lord had promised to be with them. They were exhorted to be faithful unto death, and He would give them a crown of life. Les also notes that believers will suffer tribulation, and that for the most part freedom of worship and the rights of the individual have been guaranteed in Western civilization only in the last couple hundred years.