What does Genesis 18:30 mean?
Abraham has boldly questioned whether God's plan to destroy Sodom and Gomorrah is just, since there might be righteous people living there. In this context, "righteous" does not mean moral perfection, rather it means those who did not participate in the well-known sins of the city (Ezekiel 16:49–50; Genesis 19). God graciously allows a sinful mortal like Abraham to discuss the boundaries of His mercy, even as Abraham attempts to push God's standards further and further down.Here, Abraham begs the Lord not to get angry with Him. Reading this passage with fresh eyes—knowing nothing else about God or His character as revealed in Scripture—one is likely to be concerned about Abraham's boldness, as well. Prior to this conversation, God destroyed virtually the entire race of man with a flood in Genesis 7. He has declared His intent to judge the sins of Sodom and Gomorrah (Genesis 18:17–21). We know how highly God values human righteousness, and we know what He is capable of when human beings indulge in wickedness.
Abraham, however, believes himself to be bargaining for the very life of his nephew Lot and his family. If he can get God to agree to spare the city for the sake of the right number of righteous people, perhaps Lot can be saved from God's judgment. The Lord has already agreed not to destroy the city if He finds 50, 45, or 40 righteous people there. Now the Lord agrees to 30.
Abraham, though, clearly knows how depraved this city is (Genesis 13:13; Genesis 14:22–23). He understands that 30 might still be more "righteous" people than the city can offer.