We must remember that when the church is raptured, the restraint of the Holy Spirit will be removed from the earth. The rulers of that day will target followers of Christ as they vent their anger and rebellion against God. The “testimony which they held” is likely a reference to the judgment these believers will preach. As the events of the Tribulation intensify, they will warn of even more severe judgment to come. They will preach repentance and reckoning, and they will be killed for their message.