Hebrews 13:2 gives us a rare window into an unexpected possibility: that we might encounter and interact with an angel. It’s possible that the writer of Hebrews was thinking of an encounter between Abraham, the personified Lord, and two angels who appeared as men (Genesis 18). 

All three figures—Jesus and the two angels—first appeared to be human visitors. When Abraham recognized one of them as the Lord, he persuaded them to stay so that he might provide hospitality and a meal. The Lord appeared to Abraham and Sarah to tell them that they would have a son within a year. After their meeting, the Lord departed while the two angels continued to Sodom to deliver a message of judgment (Genesis 19). If this meeting was in the mind of the writer of Hebrews, it serves as an admonition for us as well. Angels can appear in our life without us knowing who they are. Hospitality extended to strangers may be an act of kindness extended to angels.

Hospitality is incumbent upon us all (1 Peter 4:9)—even more so when the possibility exists that we might be serving angels.

We must not get so busy counting demons that we forget the holy angels.
Billy Graham