[PapaNew]

So the purpose of the Great Tribulation is twofold; discipline (purify) the people of Israel, and completely destroy the nations to which they had been scattered.

BTW, another good passage that explains six reasons in Israel and the world for the pre-crucifixion diaspora as well as the tribulation is found in Daniel 9:24:

Seventy weeks are determined upon thy people and upon thy holy city,
[1]to finish the transgression,
[2]and to make an end of sins,
[3]and to make reconciliation for iniquity,
[4]and to bring in everlasting righteousness,
[5]and to seal up the vision and prophecy,
[6]and to anoint the most Holy.

[GiovannaNicoletta]

Exactly, PapaNew.

God promised Israel these six things, and He will keep that promise and accomplish all of them during the Tribulation.