Before the end of time, there will be a short period when Satan will be free to cause great tribulation and distress to the people on earth. God has foreknowledge and has determined the future events that will take place during Satan's time on earth. Revelation was written to warn mankind what God has determined for the future. Those who have remained faithful to God will not be harmed during the tribulation and distress. Revelation and the Antichrist is the climax of the story of God's redeeming plan.
