פירוש על בראשית 19:1

שני TWO — One to destroy Sodom, the other to rescue Lot — it was he who had come to heal Abraham — whilst the third, who had come to make the announcement to Sarah, had departed as soon as he had carried out his mission (Midrash Tanchuma, Vayera 8).

ויבאו שני המלאכים סדומה בערב, even though they arrived at that city without “time” having elapsed since they departed from Avraham, (compare Berachot 4 the angel Gavriel needing two steps, and the angel Michael only one step) they remained outside the city gates, invisible, not entering and appearing to Lot until evening. The same is true of 18,22 וילכו סדומה. Avraham had concluded his dialogue with G’d already some time previously.

ויבאו…בערב. They arrived in the evening. The reason for this whole story of the angels being hosted by Lot was to afford Lot the opportunity to justify his being saved. Although Bereshit Rabbah 50,11 attributes Lot's escape to Abraham's merit, we still need to find some redeeming feature in Lot's conduct to understand the efforts made by G'd to save him. Had the angels arrived at Sodom in daylight Lot would have lacked the moral courage to offer them hospitality even by devious means.