Angels are capable of swift flight

Daniel 9:21 ... while I was still in prayer, Gabriel, the man I had seen in the earlier vision, came to me in swift flight about the time of the evening sacrifice.

Swift flight is no doubt a metaphor of some sort, a theriomorph of some description. What it identifies is the ability of Gabriel and other angels, no doubt, to travel speedily. Without the aid of machines or other helps of that sort they are able to cover huge distances in a short time.
This would seem to fit in with
Revelation 14:6 Then I saw another angel flying in midair, and he had the eternal gospel to proclaim to those who live on the earth - to every nation, tribe, language and people. 

Also Psalm 104:4 (quoted in Hebrews 1:14) He makes winds his messengers, flames of fire his servants.

Angels are holy but they lack the perfection found in God

Job 14:17, 18  If God places no trust in his servants, if he charges his angels with error, how much more those who live in houses of clay, whose foundations are in the dust, who are crushed more readily than a moth! 

Job 15:15, 16 If God places no trust in his holy ones, if even the heavens are not pure in his eyes, how much less mortals, who are vile and corrupt, who drink up evil like water! 

These parallel verses are spoken by Eliphaz the Temanite who does say things that are incorrect and so these verses may be unreliable. It may be wiser to say that Eliphaz does state a truth here and that is that although there is a holiness about the angels that is far above the greatest examples of holiness among men, nevertheless it is less than the holiness of God. He can discern an imperfection even in the holy angels.

Angels can be present in vast numbers and yet remain unseen

2 Kings 6:15-17

When the servant of the man of God got up and went out early the next morning, an army with horses and chariots had surrounded the city. "Oh no, my lord! What shall we do?" the servant asked. "Don't be afraid," the prophet answered. "Those who are with us are more than those who are with them." And Elisha prayed, "Open his eyes, LORD, so that he may see." Then the LORD opened the servant's eyes, and he looked and saw the hills full of horses and chariots of fire all around Elisha.

The horses adn chariots of fire mentioned here are learly heavenly creautres. Elish couls see them but his servant could not until his eyes were open. Fire speaks of the presence of God adn the the horses and chariots are the appropriate counterpart to a hostile Aramean army. No doubt the norm is for us not to see the angels. There is no obvious need for our eyes to be opened to the presence as Scripture confirms the fact again and again.

Angels are involved in miracles, live in heaven and have a measure of greatness

Psalm 78:25 Human beings ate the bread of angels;* he sent them all the food they could eat.

We know that there was something supernatural about the manna that the Children of Israel ate in the wilderness. It fell daily from heaven just where the people were. It had variable properties that made it rot if kept overnight except on the night before the Sabbath. Asaph here calls it the bread of angels. Now why does he call it that? Certainly, angels are spiritual beings and have no need of food. The Puritan Arthur Jackson makes three suggestions as to what Asaph may have in mind

1. Because it was provided and sent by the ministry of angels
2. Because it seemed to come down from heaven, the dwelling place of the angels
3. To set forth the excellency of this bread, that it was meat, as one would say, fit for angels, if angels needed meat.

Coming at the matter from the other end then, we remind ourselves that God delights to do his miracles through the agency of angels and that heaven is their home, there in the presence of God. They are also a useful benchmark for excellence or greatness.

* The Hebrew has mighty ones but the LXX legitimately has angels

Angels were involved in the giving of the law

Acts 7:53 you who have received the law that was given through angels but have not obeyed it.

Galatians 3:19 Why, then, was the law given at all? It was added because of transgressions until the Seed to whom the promise referred had come. The law was given through angels and entrusted to a mediator.

Hebrews 2:2 For since the message spoken through angels was binding, and every violation and disobedience received its just punishment, ...

Deuteronomy 33:2 He said: "The LORD came from Sinai and dawned over them from Seir; he shone forth from Mount Paran. He came with myriads of holy ones from the south, from his mountain slopes.
Psalm 68:17 The chariots of God are tens of thousands and thousands of thousands; the Lord has come from Sinai into his sanctuary.

Matthew Henry comments on Acts 7:53 that the law is said to be received by the disposition of angels, because angels were employed in the solemnity of giving the law, in the thunderings and lightnings, and the sound of the trumpet. It is said to be ordained by angels (Gal. 3:19 ), God is said to come with ten thousand of his saints to give the law (Deu. 33:2 ), and it was a word spoken by angels, Heb. 2:2 . This put an honour both upon the law and the Lawgiver, and should increase our veneration for both. But those that thus received the law yet kept it not, but by making the golden calf broke it immediately in a capital instance.

Barnes notes that the phrase given through angels has been supposed to mean that the Law was given “amidst” the various ranks of angels, being present to witness its promulgation. Others suppose that the angels were employed as agents or instruments to communicate the Law. All that the expression fairly implies is that the Law was given amidst the attending ranks of angels, as if they were summoned to witness the pomp and ceremony of giving “law” to an entire people, and through them to an entire world. It should be added, moreover, that the Jews applied the word “angels” to any messengers of God; to fire, and tempest, and wind, etc. And all that Stephen means here may be to express the common Jewish opinion that God was attended on this occasion by the heavenly hosts, and by the symbols of his presence, fire, and smoke, and tempest.

Angels can destroy people

1 Chronicles 21:15 And God sent an angel to destroy Jerusalem. But as the angel was doing so, the LORD saw it and relented concerning the disaster and said to the angel who was destroying the people, "Enough! Withdraw your hand." The angel of the LORD was then standing at the threshing floor of Araunah the Jebusite

1 Corinthians 10:10 And do not grumble, as some of them did - and were killed by the destroying angel.

Exodus 12:23c and he will not permit the destroyer to enter your houses and strike you down.

Acts 12:23 Immediately, because Herod did not give praise to God, an angel of the Lord struck him down, and he was eaten by worms and died. 

More than once we hear of angels involved in the act of destroying people, killing them. It is not entirely clear whether such angels may be fallen or unfallen. This appears to be what happened in David's time, although given the reference to the angel of the LORD, it may be God himself who is in mind. Paul suggests in the New Testament that a destroying angel was responsible for putting people to death in the wilderness. The destroyer of Exodus 12 is popularly thought of as the angel of death and this may be the reference here too. In Acts Herod is killed by an angel who inflicts a terrible disease on him.

Angels are always in God's immediate presence

Luke 12 8, 9 I tell you, whoever publicly acknowledges me before others, the Son of Man will also acknowledge before the angels of God. But whoever disowns me before others will be disowned before the angels of God.

Here the repeated phrase before the angels of God is another way of speaking of the immediate presence of God (see the parallel in Matthew 10:32, 33). We learn, therefore, with regard to angels, that they are always in God's immediate presence. What we also learn, however, is that believers ought to always be aware of an invisible world, the world of angels that is the world that really counts. So often we are aware of what men see and what they think but more important is what the angels see and what they think. When tempted to deny the Lord, think of the angels.
Revelation 3:5 is parallel in part
The one who is victorious will ... be dressed in white. I will never blot out the name of that person from the book of life, but will acknowledge that name before my Father and his angels.Also relevant is Luke 15:10, which we tend to think of as referring to angels but is really referring to God himself
In the same way, I tell you, there is rejoicing in the presence of the angels of God over one sinner who repents.
In Luke 1:19 Gabriel reveals that he stands always in the presence of God.