What does Genesis 50:21 mean?

In great fear, Joseph's brothers have thrown themselves to the ground before him, seeking his mercy (Genesis 50:15–18). Years after selling him as a slave (Genesis 37:26–28), they fear their father's death will inspire Joseph to finally seek revenge.

Joseph's response made it clear they don't need to be afraid. He directly and confidently leaves ultimate justice in the hands of God, and accepts that his years of suffering were—in the end—an incredible blessing. Not only did that experience cause Joseph to live the last eighty years of his life in power and comfort (Genesis 41:46; 50:26), it provided the means to save the entire nation of Israel from death (Genesis 50:19–20).

Here, Joseph effectively repeats the words he said 17 years earlier, when he first revealed he was their estranged brother (Genesis 45:5–7). Joseph arrived at the conclusion that their evil action was part of God's great plan to save many, many people from death. He has no plan to harm them or take revenge. Rather, he intends to continue to provide for them in the land of Egypt. Poignantly, Joseph mentions providing for their little ones, as well, indicating that he doesn't see this as a temporary arrangement. They have a long-term home in Egypt, so far as he is concerned.

This moment certainly turns typical human instincts upside down. The one who was wronged ends in comforting those who wronged him; the guilty ones are being cared for by the innocent person they harmed. This verse emphasizes that Joseph pointedly speaks with kindness: reassuring them in both his words and his tone that he will not harm them in the future.