Three men appeared before Abraham in the heat of the day, as he sat in the door of his tent (Genesis 18:2). These, though they had the appearance of men, were no ordinary men. At least two of these men were angels (Genesis 19:1 cf. 19:12-ff.). It seems that the third man was a Theophany, visible appearance of a member of the Godhead, in this case in human form (Genesis 18:1,2,13,22 cf. 19:1), though I do recognize that this may simply be language of agency whereby the LORD is said to have said or done something when actually He performed through the agency of another.
How would we behave if we knew that before us stood was an angelic being, or even God Almighty Himself? Abraham, without even knowing Who stood before him, demonstrate himself to be a man of hospitality (Genesis 18:1-8). Lot likewise did (Genesis 19:1-4). We would do well to emulate them in this regard. We are to be hospitable people (Romans 12:13; 1 Timothy 3:2; Titus 1:8; Hebrews 13:2; 1 Peter 4:9). Jesus said that how we treat our fellow-man is how we treat Him (Matthew 25:31-46). “In as much as you did it to one of the least of these My brethren, you did it to Me… In as much as you did not do it to one of the least of these, you did not do it to Me” (Matthew 25:40, 45).