In Christian eschatology, a period mentioned in the Olivet Discourse as a sign that would occur in end times
The Great Tribulation refers to a period of such great suffering that has never been seen before. It will immediately precede the second coming of Christ. It is said to last 1260 days which is about 3.5 years or 42 months. During this time, the church will be persecuted and Christians will be put to death if they do not worship the beast and receive his mark.