Angels appear in the Bible from the beginning to the end, from the Book of Genesis to the Book of Revelation.
The Bible is our best source of knowledge about angels - for example, Psalm 91:11, Matthew 18:10 and Acts 12:15 indicate humans have guardian angels.
An angel of the Lord appeared to St. Joseph three times in a dream to make Mary his wife, to take the Holy Family on the Flight to Egypt, and then to return to Nazareth (Matthew 1:18-2:23). Angels announce the birth of the Christ Child to the shepherds (Luke 2:14), minister to Christ after his temptation in the desert (Matthew 4:11), comfort Jesus in his agony in the garden (Luke 22:43), and proclaim his resurrection from the dead (John 20:12). Jesus Christ stated the angels of little ones continually behold the face of the Father (Matthew 18:10): this passage has been traditionally cited as biblical evidence of Guardian Angels. Angels will come with Christ on the Day of Judgement (Matthew 24:31), and the angels will separate the wicked from the just on the Last Day (Matthew 13:49), although they do not know the day of Judgement (Mark 13:32). Christ also said the children of the resurrection will be equal to the angels (Luke 20:34). God sent an angel to free the Apostle Peter after he was jailed by King Herod (Acts 12:7-11)
The Greek word ἄγγελος or "angelos" means messenger or angel. Angels are purely spiritual beings that do God's will (Psalm 103:20, Matthew 26:53). God stationed cherubim to protect the Garden of Eden after the fall of Adam and Eve in Genesis 3:24. An angel of the Lord appeared to Moses in Exodus 3:2 to lead the Israelites from captivity in Egypt to the Promised Land. God sent an angel to punish King David and the Israelites, but stopped the angel from destroying Jerusalem after King David repented and offered sacrifice to the Lord in 2 Samuel 24. When Elijah fled Jezebel after his triumph on Mount Carmel, an angel brought him food, giving him strength to meet the Lord on Mount Horeb in 1 Kings 19. An angel restored the high priest Joshua in Zechariah 3. Sometimes angels take human form, as seen in the men who appeared to Abraham and Lot in Genesis 18-19, or Raphael who appeared in human form to Tobias.
Michael as one of the leading angels is considered "Prince" of the heavenly hosts, and appears three times in the Book of Daniel (10:13, 10:21, and 12:1). He is the only one in the Bible referred to as an Archangel (Jude 1:9), and serves a major role in Chapter 12 of the Book of Revelation. The angel Gabriel first appears twice to Daniel (Daniel 8:16 and 9:21), but is best known for the Annunciation to Mary that she would be the Mother of Jesus, the Son of God (Luke 1:26-38). The Book of Tobias (Tobit) 12:15 names Raphael as "one of the seven who stand before the Lord." Revelation 8:2 also refers to the seven angels who stand before the Lord. The seven are Michael, Gabriel, and Raphael, the three named in the Bible, and Raguel, Remiel, Saraqael, and Uriel, named in Enoch 20:1-8, a book found in the Dead Sea Scrolls and in the Bible of the Oriental Orthodox Church of Ethiopia.
Thomas Aquinas was a great medieval theologian, and is known as the "Angelic Doctor" for his writings on angels in his Summa Theologica. Thomas Aquinas believed that angels, being spiritual beings, influence mankind by illuminating one's mind with an idea. Quoting Scripture, he named 9 orders of angels in 3 groups: the highest hierarchy being next to God, Seraphim (Isaiah 6:2), Cherubim (Genesis 3:24, Ezekiel 10:1-22), and Thrones (Colossians 1:16); the middle hierarchy involved in government, Dominations (Colossians 1:16), Virtues (1 Peter 3:22), and Powers (Colossians 1:16); and the third hierarchy involved in work, Principalities (Colossians 1:16), Archangels (1 Thessalonians 4:16), and Angels. Here are a few of the more noted Scriptural passages on Angels.
"The man gave his wife the name “Eve,” because she was the mother of all the living.
The Lord God made for the man and his wife garments of skins, with which he clothed them.
Then the Lord God said: See! The man has become like one of us, knowing good and evil!
Now, what if he also reaches out his hand to take fruit from the tree of life, and eats of it and lives forever?
The Lord God therefore banished him from the garden of Eden,
to till the ground from which he had been taken.
When he expelled the man, he settled him east of the garden of Eden;
and he stationed the cherubim and the fiery revolving sword,
to guard the way to the tree of life."
"And Jacob went out from Beersheba, and went toward Haran.
And he lighted upon a certain place, and tarried there all night, because the sun was set.
And he took of the stones of that place, and put them for his pillows, and lay down in that place to sleep.
And he dreamed, and behold a ladder set up on the earth, and the top of it reached to heaven;
and behold the angels of God were ascending and descending on it!"
"Behold, I send an angel before you, to guard you on the way and to bring you to the place which I have prepared.
Give heed to him and hearken to his voice, do not rebel against him, for he will not pardon your transgression; for my name is in him.
But if you hearken attentively to his voice and do all that I say, then I will be an enemy to your enemies and an adversary to your adversaries.
"I am the angel Raphael, one of the seven who stand before the Lord."
Book of Tobias (Tobit) 12:15
"The angel of the Lord, who encamps with them, delivers all who fear God."
"For God commands the angels to guard you in all your ways.
With their hands they shall support you,
lest you strike your foot against a stone."
Angel of God, my guardian dear,
To whom God's love commits me here
Ever this day be at my side
To light and guard, to rule and guide. Amen.
Nebuchadnezzar responded and said, “Blessed be the God of Shadrach, Meshach and Abednego, who has sent His angel
and delivered His servants who put their trust in Him, violating the king’s command,
and yielded up their bodies so as not to serve or worship any god except their own God.
Daniel 3:28 (95)
"Then, at break of day, the king arose and went in haste to the den of lions.
When he came near to the den where Daniel was, he cried out in a tone of anguish and said to Daniel,
"O Daniel, servant of the living God, has your God, whom you serve continually, been able to deliver you from the lions?"
Then Daniel said to the king, "O king, live for ever! My God sent his angel and shut the lions' mouths, and they have not hurt me,
because I was found blameless before him; and also before you, O king, I have done no wrong."
"Now the birth of Jesus Christ took place in this way.
When his mother Mary had been betrothed to Joseph, before they came together she was found to be with child of the Holy Spirit;
and her husband Joseph, being a just man and unwilling to put her to shame, resolved to send her away.
But as he considered this, behold, an angel of the Lord appeared to him in a dream, saying,
"Joseph, son of David, do not fear to take Mary your wife, for that which is conceived in her is of the Holy Spirit;
she will bear a son, and you shall call his name Jesus, for he will save his people from their sins."
"In the sixth month, the angel Gabriel was sent from God to a town of Galilee called Nazareth,
to a virgin betrothed to a man named Joseph, of the house of David,
and the virgin's name was Mary." And coming to her, he said,
"Hail, Full of Grace! The Lord is with you."
And in that region there were shepherds out in the field,
keeping watch over their flock by night.
And an angel of the Lord appeared to them,
and the glory of the Lord shone around them,
and they were filled with fear.
And the angel said to them, "Be not afraid;
for behold, I bring you good news of a great joy which will come to all the people;
for to you is born this day in the city of David a Savior, who is Christ the Lord.
And this will be a sign for you:
you will find a babe wrapped in swaddling cloths and lying in a manger."
And suddenly there was with the angel
a multitude of the heavenly host praising God and saying,
"Glory to God in the highest, and on earth peace among men with whom he is pleased!"
"After withdrawing about a stone’s throw from them and kneeling, he prayed, saying,
“Father, if you are willing, take this cup away from me; still, not my will but yours be done.”
And to strengthen him an angel from heaven appeared to him.
He was in such agony and he prayed so fervently that his sweat became like drops of blood falling on the ground.
When he rose from prayer and returned to his disciples, he found them sleeping from grief."
"But Mary stood weeping outside the tomb. As she wept, she bent over to look into the tomb;
and she saw two angels in white, sitting where the body of Jesus had been lying, one at the head and the other at the feet.
They said to her, “Woman, why are you weeping?”
She said to them, “They have taken away my Lord, and I do not know where they have laid him.”
When she had said this, she turned around and saw Jesus standing there, but she did not know that it was Jesus.
Jesus said to her, “Woman, why are you weeping? Whom are you looking for?”
Supposing him to be the gardener, she said to him, “Sir, if you have carried him away,
tell me where you have laid him, and I will take him away.”
Jesus said to her, “Mary!” She turned and said to him in Hebrew, “Rabbouni!” (which means Teacher).
Jesus said to her, “Do not hold on to me, because I have not yet ascended to the Father.
But go to my brothers and say to them, ‘I am ascending to my Father and your Father, to my God and your God.’”
"The very night when Herod was about to bring him out, Peter was sleeping between two soldiers,
bound with two chains, and sentries before the door were guarding the prison;
and behold, an angel of the Lord appeared, and a light shone in the cell;
and he struck Peter on the side and woke him, saying, "Get up quickly."
And the chains fell off his hands. And the angel said to him, "Dress yourself and put on your sandals."
And he did so. And he said to him, "Wrap your mantle around you and follow me."
And he went out and followed him; he did not know that what was done by the angel was real, but thought he was seeing a vision.
When they had passed the first and the second guard, they came to the iron gate leading into the city.
It opened to them of its own accord, and they went out and passed on through one street; and immediately the angel left him.
Acts of the Apostles 12:6-10
"Let brotherly love continue.
Do not neglect to show hospitality to strangers,
for thereby some have entertained angels unawares."
"When the Lamb opened the seventh seal, there was silence in heaven for about half an hour.
Then I saw the seven angels who stand before God, and seven trumpets were given to them.
"Then war broke out in heaven; Michael and his angels battled against the dragon.
The dragon and its angels fought back,
but they did not prevail and there was no longer any place for them in heaven.
The huge dragon, the ancient serpent, who is called the devil and Satan,
who deceived the whole world, was thrown down to earth,
and his angels were thrown down with him."
Then the angel said to me, “Write this: Blessed are those who are invited to the wedding supper of the Lamb!"
And he added, "These are the true words of God."