What does Genesis 18:23 mean?

The Lord has revealed to Abraham His plans to investigate the sinfulness of the cities of Sodom and Gomorrah and, by implication, execute judgment upon them if they are guilty. This is entirely for man's benefit, since God already knows what is happening. Rather, by speaking of "investigation," and conversing with Abraham, God is teaching mankind by giving us a clear, unmistakable justification for what He is about to do.

Abraham certainly knew of the wickedness of these cities (Genesis 13:13; Genesis 14:22–23). Not only would they have had a reputation in the region for their behavior, but Abraham's nephew Lot and his family also live in the city, among the people. Abraham is concerned that Lot will suffer the same fate as the rest of the city if the Lord chooses to take action against them. This seems to be his motivation for asking God to spare the city.

Abraham begins to question the Lord about what will happen. Will He "sweep away the righteous with the wicked?" In other words, will God allow innocent people to be hurt in His judgment of the guilty? This is a question many still ask about the Lord. Is He just? What are the boundaries of His mercy? What will keep Him from delivering His righteous wrath on those who are guilty of grave sins? As human beings, we recoil at the idea of those we perceive as "innocent" being caught up in God's wrath against those we perceive as "guilty."

The following verses will reveal that Abraham desperately wants for the Lord to quantify His mercy with a specific number.