Commentary for Genesis 18:17

המכסה אני SHALL I HIDE? This is a question.

AND THE ETERNAL SAID. I.e., to the host of heaven standing by Him,¹¹¹See I Kings 22:19. or to the angel messengers.
It is possible that the word amar (He said) refers to thought, meaning that He thought He should not keep it hidden from Abraham on account of these reasons. Similarly: I ‘said,’ in the noontide of my days I shall go;¹¹²Isaiah 38:10. The word “said” here means “thought.” And he ‘said’ to slay David.¹¹³II Samuel 21:16. Here too the word “said” means “thought.” Likewise all expressions of speaking within the heart refer to thought.¹¹⁴E.g., And Esau said in his heart, further, 27:41. See Ramban there.

המכסה אני מאברהם, the fact that I am about to overturn Sodom and its satellite towns. G’d reasoned seeing that Avraham was sure to tell his descendants of G’d’s promise to him to give the whole land of Canaan to his descendants, He would diminish these descendants’ inheritance by utterly destroying these towns and the valley which were part of area promised to the Jewish people as an inheritance. He therefore felt duty-bound to obtain Avraham’s consent of what He was about to do. We had learned in Genesis 10,19 that the boundaries of the Canaanite extended to regions that included the Jordan valley. G’d considered it inappropriate to deny Avraham fulfillment of part of His promise by making these parts of the land of Canaan totally useless to its inhabitants.