John Calvin Commentary Genesis 18:20

"And Jehovah said, Because the cry of Sodom and Gomorrah is great, and because their sin is very grievous;" — Genesis 18:20 (ASV)

The cry of Sodom. The Lord here begins more clearly to explain to Abraham his counsel concerning the destruction of the five cities, although he only names Sodom and Gomorrah, which were much more famous than the rest. But before he makes mention of punishment, he brings forward their iniquities, to teach Abraham that they justly deserved to be destroyed; otherwise, the history would not serve for instruction.

But when we perceive that the anger of God is provoked by the sin of man, we are inspired with a dread of sinning.

In saying that the “cry was great,” he indicates the grievousness of their crimes, because although the wicked may promise themselves impunity by concealing their evils, and although these evils may be silently and quietly borne by people; yet their sin will necessarily sound aloud in the ears of God.

Therefore, this phrase signifies that all our deeds, even those of which we think the memory to be buried, are presented before the bar of God, and that they, even by themselves, demand vengeance, although there should be none to accuse.