Heb 13:2: “Do not forget to entertain strangers, for by so doing some have unwittingly entertained angels.”

Throughout the Old Testament “the angel of God” or angels came to certain men to deliver them a message from God, for direction or correction, or to rescue them from harm (more often they were behind the scenes).

There are times men are compared to, or called as angels or have the wisdom of an angel or angel of the Lord.

2 Sam. 14:17 Your maidservant said, 'The word of my lord the king will now be comforting; for as the angel of God, so is my lord the king in discerning good and evil.”

1 Sam 29:9 Then Achish answered and said to David, "I know that you are as good in my sight as an angel of God.”

Sometimes the angels were seen 1 Chron. 21:20 “Now Ornan turned and saw the angel.” Sometimes they only heard the message. It is the angel of the Lord that appears to man almost unanimously in the old testament.

To entertain angels have a number of meanings. It can mean real non earthly beings disguised as men that bring a message from God, which often happened in the Old Testament and occasionally in the New Testament. But they announced themselves and it was always evident that they were different. And men often first reacted with fear (Mt.28:2; Lk.1:11; 2:9; Acts 27:23). There other times it does not describe men’s reaction (Acts 8:26; 12:7)

When the angel of God (the Lord) appeared one would know it, it was not entertaining unaware.

Judges 13:6 ‘So the woman came and told her husband, saying, "A Man of God came to me, and His countenance was like the countenance of the Angel of God, very awesome; but I did not ask Him where He was from, and He did not tell me His name.”