13:20 shortened those days. As described in Revelation 6, 8, 9, 13 and 16, both the persecutions of the Antichrist against believers and the plagues unleashed by God against unbelievers in the coming tribulation period would result in depopulating the entire world if they continued indefinitely. But God has ordained that the whole period will only last seven years (see on Daniel 9:25), with the most intense destruction in the last half of that period (Daniel 9:26; Revelation 11:2; 13:5).
13:20 elect’s. The “elect” are the same as the ones “whom He hath chosen” in this passage. Even during the awful tribulation period, God will preserve a remnant of believers alive to enter the great millennial kingdom age following the tribulation. Matthew used only the single word “elect” in reporting this promise of Christ, but Mark indicated further that, in the context of the tribulation, “elect” and “chosen of God” are synonymous terms.