(17) Now God said, “Shall I hide from Avraham what I am about to do, (18) since Avraham is to become a great and populous nation and all the nations of the earth are to bless themselves by him? (19) For I have singled him out, that he may instruct his children and his posterity to keep the way of God by doing what is just and right, in order that God may bring about for Avraham what He has promised him.” (20) Then God said, “The outrage of Sedom and Amorrah is so great, and their sin so grave!

What I am doing in Sodom. It is not proper for Me to do this thing without his knowledge. I gave him this land and these five cities therefore are his — as it is said, “And the territory of the Canaanites was from Sidon … as you go towards Sedom and Ammorah etc.” I called him Avraham, the father of a multitude of nations; should I destroy the children without informing the father who loves me?

ואברהם הולך..וה' אמר. He was busy with Commandments of Loving Kindness, such as accompanying guests on their way. This is the meaning behind the words למען אשר יצוה את בניו וג'; if Avraham saw that God had revealed His plans for Sodom to him, immediately after he accompanied the angels, he would understand that the performance of such kind deeds resulted in one’s gaining an ever more intimate relationship with God. He would be encouraged to instruct his children, etc., to act in this manner. This is what is meant in Avot 4,2 שכר מצוה מצוה, “the reward of performing a mitzvah is .that one will be encouraged to perform another mitzvah.

And Avraham shall become. Midrash Agadah comments: The memory of the righteous shall be for a blessing. Since He mentioned Avraham, He blessed him. The simple meaning of the verse though is, “Shall I conceal it from him since he is so beloved by Me to become a mighty nation?” Thus the language of Rashi.

The correct interpretation is that God, blessed be He, spoke of the honor of Avraham, saying: “Behold, he is destined to become a great and mighty nation, and his memory will be a blessing among his seed and all nations of the earth. Therefore, I shall not conceal it from him for the future generations will say, “How could He hide it from him?’

or, ‘How could the righteous one be so callous about his close neighbors and have no mercy on them, not praying at all in their behalf, and that which was known to him, [i.e., that the cities will be destroyed], was good and pleasing!’

For I know that he recognizes and is cognizant that I the Eternal love righteousness and justice, that is to say, that I do justice only with righteousness, and therefore he will command his children and his household after him to follow in his path.

Now if it is possible in keeping with righteousness and justice to free the cities from destruction, he will pray before Me to let them go, and it will be well and good. And if they are completely guilty, he too will want their judgment. Therefore, it is proper that he enter in the council of God.”

For I know him — this is an expression denoting "affection"...

Still the primary meaning of these terms connected with the root ידע is really that of knowing, for whoever holds a person in affection attaches him to himself, so that he knows him well and is familiar with him. And why do I hold him dear?

כי ידעתיו, “for I know him intimately,” The root ידע is used here in the sense of bestowing recognition on someone.

Alternatively, the meaning of the word is that “I have supervised him closely.” When God “knows” a person this implies that He keeps careful track of all that this person does and He protects him. The words כי ידעתיו single out Avraham from other ordinary human beings who do not enjoy the constant supervision by God of what they do and what happens to them.

The righteous enjoy this advantage over their secular-oriented fellow human beings. You should appreciate that God operates in this universe by means of both השגחה כללית and השגחת פרטית, “supervision of a general kind,” and “supervision of a particular, personal kind.”