What does Genesis 18:26 mean?

Abraham's tone in the previous verses seems indignant, and even scheming. God is discussing the sins of Sodom and Gomorrah, implying that judgment was coming on those cities for their outrageous depravity. Abraham's nephew Lot lived in Sodom. Abraham pointedly asked the Lord if He would sweep the righteous away with the wicked. What if 50 righteous people lived in Sodom? Would God still destroy the city? Abraham made it personal: Far be it from you! Shouldn't the judge of all the world be fair? This, of course, implies that Abraham has the right to judge God's character according to his own perspective.

How would God respond to such a comment from a limited, sinful mortal? Knowing nothing else about God, or the Scriptures, one would half-expect God to crush Abraham for being so insolent about His character. Instead, the Lord responds in the most gracious way we could imagine. He simply agrees: If I find 50 righteous people, I will spare the whole place. This, as with His prior comments about "investigating" the cities, are merely for our benefit. God does not need our approval or our understanding. And yet, in this incident, He gently allows us to see that His decision, in this case, is entirely just.

The following verses will reveal, though, that Abraham's not done. He's up to something, most likely related to his concerns for his nephew, Lot.