Mt 24:29-31, Mk 13:27
In the Old Testament, Isaiah prophesied that God would gather God's children on that day. (Isa 27:12-13)
Isa 27:12 And it shall come to pass in that day, that the Lord shall beat off from the channel of the river unto the stream of Egypt, and ye shall be gathered one by one, O ye children of Israel. 13 And it shall come to pass in that day, that the great trumpet shall be blown, and they shall come which were ready to perish in the land of Assyria, and the outcasts in the land of Egypt, and shall worship the Lord in the holy mount at Jerusalem.
When Jesus, the Christ, comes back to this earth, he will gather the children of God. (Mt 24:29-31, Mark 13:27)
Mt 24:29 Immediately after the tribulation of those days shall the sun be darkened, and the moon shall not give her light, and the stars shall fall from heaven, and the powers of the heavens shall be shaken: 30 And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory. 31 And he shall send his angels with a great sound of a trumpet, and they shall gather together his elect from the four winds, from one end of heaven to the other.
Mark 13:27 And then shall he send his angels, and shall gather together his elect from the four winds, from the uttermost part of the earth to the uttermost part of heaven.