Commentary for Genesis 50:20

אלוקים חשבה לטובה, you were the unwitting agents of G’d and you are therefore not to blame. G’d had planned that it should all be for the good.

ואתם חשבתם עלי רעה, you had mistakenly considered me as a רודף, someone threatening your very lives. Had you not erred, your actions would have been perfectly justified.

ואתם חשבתם עלי רעה, והאלוקים חשבה לטובה, "what you had planned as harm for me, G'd planned it for good, etc." The whole matter is comparable to that of a person who plans to give his friend a poisoned drink in order to kill him, but who mistakenly pours him a cup of wine. Legally speaking, such a person is not guilty before a human tribunal. Similarly, the brothers were not guilty before Joseph though they were guilty before a Heavenly Tribunal. It is possible that the forgiveness of the victim even to a Jewish criminal would not free the criminal from the death penalty if the deed had been committed under circumstances warranting such a verdict.

Elokim meant it for good. Hashem arranged for them to suspect him and try to harm him in order to bring about this great event, otherwise Yaakov’s righteous sons would never have done such a deed.

אלקים חשבה לטובה, G’d exploited your error for something good.