Rashi on Genesis 18:16/רש"י על בראשית י״ח:ט״ז

1וישקיפו [AND THE MEN] GLANCED — Wherever the Hiphil form of שקף occurs in the Scriptures it denotes taking notice for the purpose of bringing evil (Midrash Tanchuma, Ki Tisa 14), except (Deuteronomy 26:15) (a passage dealing with the tithe, including that given to the poor), “Look forth (השקיפה) from thy holy habitation . .. [and bless thy people] for so great is the power (virtue) of giving to the poor that it changes God’s anger into mercy.

2לשלחם means TO ESCORT THEM, for he believed that they were travellers.