Chapter 13:26 Then they will see the Son of Man coming in clouds with great power and glory.
Chapter 13:27 And then He will send forth the angels, and will gather together His elect from the four winds, from the farthest end of the earth to the farthest end of heaven.
In verse 27, we see the phrase His elect which in this case are those who believe during the seven-year tribulation period. The elect of the church will already have been taken to heaven before the tribulation begins. The word elect is used in various ways: to signify on Christ (Isa. 42:1; I Peter 2:6), Israel (Isa. 45:4), millennial saints (Isa. 65:22), tribulation saints (which is this reference, church saints (Col:3:12) and angels (I Tim.5:21).