For pre-tribulationists they get the seven years mostly by the way they interpret the 70th week of Daniel in Daniel 9:22-27. They believe that each week is 7 years, and that the final week is the Great Tribulation. They believe in what is called a gap theory, meaning that the first 69 weeks began with King Artaxerxes and it ended at the death of Christ, and that the Church age being a mystery to Daniel led to him not to prophesy concerning which leaves a gap period, and then Daniel jumps to the time of the Antichrist and prophesies that age as the 70th week.
As for a Catholic perspective, the gap theory is rejected. As for the time when the 70 weeks begins is not actually that important because many great scholars have calculated it out with various results. In my opinion I accept that it probably began with King Artaxerxes, but by rejecting the gap theory I believe the 70 weeks ended at the at the death of Christ. Theodoret the Bishop of Cyrus gave the interpretation that I accept for the final week.
Daniel 9:27
**And he shall confirm the covenant with many for one week; **
The new covenant will be given to the believers in this week, and He will fill them with all power.
**and in the midst of the week he shall cause the sacrifice and the oblation to cease. **
sacrifice according to the law will come to an end when the true sacrifice of the innocent lamb, who takes away the sin of the world, is offered; when it is finally offered, the other will cease.
**And for the overspreading of abominations he shall make it desolate, **
that is, that formerally venerable and fearsome place will be made desolate. A sign of the desolation will be the introduction into it of certain images forbidden by the law; Pilate was guilty of this by introducing into the divine temple by night the imperial images in violation of the law (according to Josephus Ant. 18.55-59).
In case the Jews should think the divine temple would recover its former splendor and glory, he consequently added…
even until the consummation, and that determined shall be poured upon the desolate."
until the end of the age the consumation of the desolation will continue, undergoing no change.
