Genesis 18:21

I will now appear, and see whether, as the cry of a damsel torn away, which ascendeth before Me, they have made completion of their sins; (or, whether they have made an end of their sins;) and if they have wrought repentance, shall they not be as (if) innocent before Me? and as if not knowing, I will not punish.

And if not, I know... For in truth G-d is called Everything because Gd includes everything and everything is included in Him, and the persons are called "a piece" for we are only a part of the creation. This is why He is the only one that is fit to examine the persons' heart and also know the actual persons' actions in a way that is complete and not partial like the human way. Therefore in this same perasha in verse 23 Abraham said to G-d "Will You sweep away the innocent along with the guilty?"... because Abraham could only see a part of the situation and not the whole.

עשו כלה, the vertical line after the word עשו is like a comma between these words, i.e. “if they have done as reported, I will put an end to them.”

ארדה נא, I will examine where their wickedness will eventually lead to, similar to the considerations which guided G’d in Genesis 11,7 when the destruction of the Tower was decreed and the splitting up of the languages and habitats of people, in order to make it unnecessary to destroy mankind as had happened before the deluge.

ואראה הכצעקתה, I want to examine this in action, i.e. how they will behave when Lot volunteers to host the angels, and if they will attack him. If that happens, the whole world will know that they fully deserved their punishment.

עשו כלה, they are all involved in this sin, without anyone protesting such behaviour. We find a similar meaning of the word כלה in Exodus 11,1 כלה גרש יגרש, where G’d tells Moses that after the next plague Pharaoh would not only let the Israelites go but would expel every last one of them. This proof of how justified G’d was in bringing destruction on these towns would also be confirmed by means of the angels. The Torah testifies that the assault on Lot and his guests included כל העם מקצה, “all the people from every corner.” (19,4)

ארדה נא ואראה, we explained the meaning of G’d’s “descending” already on 11,5. This time the text says ואראה, “I shall see,” instead of לראות, “to see.” The Torah writes in this vein although we know that G’d is perfectly aware of all that goes on here on earth. The reason why the Torah describes G’d’s activity in this manner is only to remind people on earth that He is not in a hurry to mete out retribution, but is patient, and even when His patience is exhausted, He does not act impetuously, but is always in complete control. He examines if there is any way in which delaying retribution can be justified. It was this very phrase which provided Avraham with an opening to engage G’d in a dialogue concerning His Justice and man’s perception of Divine justice. He did this not because he doubted G’d’s justice, but in order to be able to teach man something about how G’d’s justice works.

הכצעקתה, if in accordance with the outcry that has come to My attention, they have indeed done, כלה, they deserve to die, but if not, אדעה, I will know about it, and I will welcome the fact that Avraham appreciates this and will ask Me about how I administer justice. The mappik heh is a hint that Sodom was the city which determined the fate of the others. Its satellites patterned their lifestyles on that of the city of Sodom. A comment in the Midrash (quoted by Rashi) suggests that the mappik heh underscores a specific incident in which a young girl who had a soft heart and gave bread to a stranger was found out and punished most cruelly, being smeared with honey and suspended between two trees, so that the bees killed her in the process of licking the honey off her body.