What does Genesis 20:4 mean?

God is speaking to Abimelech in a nighttime dream. God has told Abimelech, the king of Gerar, that he will die from his current illness (Genesis 20:3) for taking a married woman as his wife. Abimelech now pushes back: He had not yet approached Sarah. He asks if God would kill "an innocent people"—the only reason he has taken Sarah is the assumption that she was not married.

To his credit, Abimelech appears to be concerned not just about himself but also about his people, who may have been sick, as well. He seems to assume that God's judgment will include more than just the king. That makes more sense when, at the end of this chapter, we learn that God has stopped any of the women in Abimelech's household from bearing children.

Abimelech's question about God's character, whether the Lord would kill innocent people, echoes Abraham's question to the Lord about whether He would destroy righteous people in His judgment of Sodom (Genesis 18:23). In both cases, the answer was "no." God's character remains intact throughout these moments. This not only highlights the righteousness of God, it would have been a cutting point for Abraham to hear. His own actions put the innocent at risk, though he had appealed to God for the sake of the innocent in Genesis chapter 18.