FOUR ACTIONS HAVE THE POWER TO CHANGE A HEAVENLY DECREE
- Tzedakah - Giving Charity
- Tefillah - Prayer
- Teshuvah - Improving one's deeds
- Shinui Shem - Being renamed
Some add:
- Shinui Hamakom - Changing residence
We learn this last point from the fact that Hashem told Avram, "Go out rom your land, etc. and I will make of you a great nation." Avram only merited children after changing his residence.
Moving to a strange place helps annul a Heavenly decree since a man's heart is humbled when he is exiled from his home.
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Source: Midrash Says