Do not neglect hospitality, because through it some have entertained angels without knowing it.
Before there was a planet, a person, or a problem, there were angels. Unlike us humans who can trace our ancestry back back to one man and one woman, angels are not a race, they are a company (they do not reproduce themselves). They can travel at the speed of light. They can alter their appearance and even 'appear' invisible. This enables them to interact with us humans in ways that we might not always recognise.
The author of Hebrews states this rather too a-matter-of-fact-ly. I would have welcomed him to have explained what he meant in Hebrews 13:2 that some believers had hosted angels without realising it. He stated in the previous chapter that the Church had a direct heavenly link to "innumerable angels". I would have liked that one explained a bit further as well. It seems that the early church experienced the company of angels of an all-too-frequent basis. When things got tough for the Church, it was often angels who rescued them. Just because something or someone is invisible doesn't mean they are imaginery. Angels could transform their supra-reality into the less-real physicality of human beings. We see them singing over the birth of Jesus. We see them in the desert ministering sustanance to Jesus. We see them outside the tomb of Jesus presumably having just thrown a several tonne boulder away from the mouth of the entombing cave. We see them at the ascension of Jesus. We see them busting open prisons to free near-despairing apostles. We hear reports of them apparently giving strange doctrines to wandering preachers which caused the Apostle Paul to warn against such false teaching - but not against the idea that angels appear to believers! Then we are overwhelmed when we are given just a sneak peak into Revelation's Heaven where we are awed by 100 trillion mighty angels in one sector of heaven who apparently form a sampling of their total number!
The majestic creatures we call angels are not the pathetically cute little flying babies we often see wearing nappies and having wings on their backs. Neither are they erotic catwalk models - in fact, there is no hint that there are any female angels (sorry Google). These splendid creatures are described in the Bible as tall, strong, and no-nonsense. On nearly ever occasion they appear to people in the Bible, they induce great fear. "Fear not", is usually the first thing they have to say to those they appear to (eg. Daniel 10:12). Sometimes they are described as having wings, but generally not. They are ordered into different varieties with different aspects of the divine mission. We observe in Scripture messenger-angels, guardian-angels, military-angels, worship-leading angels, and executive angels. These created beings exist to serve (the Bible word for serve is 'minister') their Creator. He commissions them to intervene in the affairs of man so that His plan of redemption is sovereignly stewarded.
¶ Of the angels he says,
"He makes his angels winds,
and his ministers a flame of fire."
You may never know how often God has used angels to rescue, instruct, or correct you. Chances are that everytime you pray both your prayer and its answer have something to do with the involvement of angels. We don't have to pray or talk directly to angels - and indeed we shouldn't - because we have the privilege that angels can't understand, of being invited to pray directly to God through Christ.
It was revealed to them that they were serving not themselves but you, in the things that have now been announced to you through those who preached the good news to you by the Holy Spirit sent from heaven, things into which angels long to look.
First Peter 1:12
Your praying is not in vain. Your enduring faith is not in vain. Your love for Christ's Church is not in vain. Your devotion to the Scriptures is not in vain. In each of these spiritual exercises there are often angels actively involved.
TYPES OF ANGELS
Messenger Angels are counted in the "myriads" (billions of trillions). They carry out God's mission of spreading His glory through divinely authorised interventions in the affairs of mankind. Despite the cute airbrushed artwork, there is no Biblical record of angels having wings and there is only two references of messenger angels "flying" in Scripture (Rev. 14:6; 19:17). They can change their appearance to appear human (Gen. 19:1). They can communicate with humans without "speaking", that is, by telepathy - especially via dreams (Matt. 1:20). The word 'angel' actually means messenger.
¶ Now when they had departed, behold, an angel of the Lord appeared to Joseph in a dream and said, "Rise, take the child and his mother, and flee to Egypt, and remain there until I tell you, for Herod is about to search for the child, to destroy him."
Archangels (Greek, arkhos which means "chief") are military angels who lead hosts of messenger angels into battle (Rev. 12). Jewish legend states that there are 7 archangels although the Bible only names two of them, Michael (Jude 9) and Gabriel (Luke 1:26). Archangels are greater in power than messenger angels. Archangels are described as flying and presumably appear to humans as if they have wings. They also appear with a brandished sword to humans (and animals, note Numbers 22:23). When the very last battle begins, it will be announced by an archangel (note the rules of war includes the sounding of a warning trumpet to alert the enemy, Num. 10:9). According to one of them, Gabriel, they stand at attention in the presence of God awaiting to be sent to carry out His redemptive mission.
For the Lord himself will descend from heaven with a cry of command, with the voice of an archangel, and with the sound of the trumpet of God. And the dead in Christ will rise first.And the angel answered him, "I am Gabriel. I stand in the presence of God, and I was sent to speak to you and to bring you this good news."
First Thessalonians 4:16
Cherubs (or, "cherubim" - the Hebrew language adds 'im' where English ordinarily adds 's') are the most powerful angels. They are fierce, incredibly terrifying, and undefeated. Revelation 4 describes tells us that there are four of these creatures. Revelation and Ezekiel tell us that they have the characteristics of a lion, a bull, an eagle, and a man. They have the ability to move wherever they need to go without turning. They are super large. God described as having His throne borne by cherubim (Ps. 99:1). Wherever God goes, cherubim surround Him (Ps. 18:10). They have four wings each and when they fly the size of their wings produce a sound louder than a 747 jumbo jet.
As for the likeness of their faces, each had a human face. The four had the face of a lion on the right side, the four had the face of an ox on the left side, and the four had the face of an eagle.And the sound of the wings of the cherubim was heard as far as the outer court, like the voice of God Almighty when he speaks.
When Adam plunged the human race into certain damnation by falling for the lie of Satan (a fallen angel) that He could make up his own rules for how to live, God banished Adam and Eve from the Garden of Eden and placed cherubim at the entrance to keep man from entering and partaking of the Tree of Life (Gen. 3:24). Thankfully today we can take up God's offer of avoiding eternal damnation and eat freely of the Tree of Life by surrendering our lives to Him and trusting Christ as our Saviour who has borne our eternal damnation and overcome it.
Seraphim are the most majestic of God's heavenly beings. The hover above God's throne and lead heaven in worship. They are described as having 6 wings where two of these wings are used to cover their faces from beholding God's unfiltered glory. These two awesome beings can be seen from anywhere in heaven. They are a reminder to anyone who seeks to know God that the closer you want to come to God the more you will be drawn into worship of God and the more you will crave His glory and not your own will.
Above him stood the seraphim. Each had six wings: with two he covered his face, and with two he covered his feet, and with two he flew. And one called to another and said:
"Holy, holy, holy is the LORD of hosts;
the whole earth is full of his glory!"
¶ And the foundations of the thresholds shook at the voice of him who called, and the house was filled with smoke.
As powerful as angels are, there are certain things that bewilder them. Why would the Omnipotent One condescend to became a weakling? Why would GOD offer to elevate these rebellious weaklings to adoption as sons of God? Why would the Creator invite weaklings to approach Him anytime after they have received His Spirit of sonship? But most bewilderingly, if the Maker is offering an escape from certain eternal damnation for the treason of self-deification, why don't more weaklings accept this "can't-lose" offer? Have you? Angels are watching.
...in the things that have now been announced to you through those who preached the good news to you by the Holy Spirit sent from heaven, things into which angels long to look.
First Peter 1:12