What can you tell me about angels in the Bible? Who are they, where do they come from and what exactly do they do? What can you tell me about Nephilim, Elohim, Seraphim and Cherubim?
Genesis 1:1 opens with, "In the beginning God created the heavens and the earth." In the middle of the verse are the Hebrew letters, Aleph and Tav, which are the first and last letters of the Hebrew alphabet. These two letters are ignored in English translations because they don't seem to have any grammatical purpose, but they correspond with the Alpha and the Omega, the first and the last, the all that there is. Jesus was not a created Being, He is a Person of God, so those two letters are not referring to Him, but to the fact that God created everything--the all that there is. The Hebrew word, "bara," translated into English as "created," is a specific kind of creation in which something is made from nothing.
So the literal translation of that verse reads, "Beginning made from nothing Elohim (the Name of God translated "God") Aleph Tav the heavens and the earth, or the sky and the land," or in English grammar, "In the beginning God made all that exists from nothing."
This verse is packed with a huge amount of information. For the purpose of answering your question the specific information we get from this verse is that because of the insertion of the Aleph and Tav into the middle of the verse we know in the beginning God created everything, which includes the angels. They have not always existed, they are created beings. And, when God began to creating He made everything, including the angels, and made it all from nothing.
Before God created anything He was the only Being anywhere. He is Spirit and until He created it, there was no matter or any other spirits in existence.
Cherubim are described in Ezekiel 1. In Revelation 4, John sees "living creatures" which are strikingly similar except he mentions only one face and 6 wings as opposed to the four Ezekiel listed. Ezekiel also calls the cherubim "living creatures." It's possible that John only saw one face on each and didn't see the others and Ezekiel saw only 4 wings and didn't see the other two. Rather than rendering these two accounts as untruths, they actually confirm that these are eye witness accounts. Most any cop will tell you, eye witness accounts do not agree on details--unless the eye witnesses have concocted a story before hand.
Ezekiel 28 and Isaiah 14, both beginning with verse 12, describe the power behind earthly thrones, which is Satan, who was created a cherub. From these passages we learn that he was anointed by God, that he served as the highest ranking angel in Heaven, that God loved him and created him perfect until he became full of himself and decided he could take God's throne away from Him. Jesus says in Luke 10:18, "I saw Satan fall like lightning from heaven." We learn from Ezekiel and Isaiah that God exiled Satan to planet earth, the garden he once tended as head honcho for God, caring for His favorite planet.
As the first God-hater, Satan enters the Garden of Eden where he serves the purpose of giving God's human beings someone to choose other than God. If a person doesn't have a choice, what's the use of free will? He manages to trick Eve and Adam just stands there and watches. When Eve gives him the forbidden fruit, he eats of it. Milton, the author of "Paradise Lost," thought Adam ate the fruit because he was afraid he would lose Eve. Regardless of his motivation, from that point on some of Satan's rebellious nature entered into the nature of human beings. Paul tells us that Satan masquerades as an angel of light, II Corinthians 11:14. He also alludes to the demonic hierarchy in a couple of places, one of those Scriptures is Ephesians 1:21.
Matthew 4 and Luke 4 describes the temptation of Jesus. An interesting point we can derive from this account is that while he wheels and deals with Jesus, Satan claims to have kingship over the kingdoms of the earth. He offers them to Jesus and Jesus doesn't argue that point with him. We know that satan's claim to be ruler of earthly kingdoms is true, from our own experience living in places or hearing about places where God is not King. And from Isaiah and Ezekiel, also from Daniel who describes how he prayed for weeks to receive an answer from God and when an angel finally appears, the angel explains that he was detained doing battle with the "prince of the Persian kingdom" and only prevailed when the Archangel Michael came to his aid. Daniel calls Michael "one of the chief princes," Daniel 10. (You can research the Hebrew nouns found in these verse on Biblehub.com. Just enter the Scripture verse reference in the site's search engine and select "Hebrew" from the list of tabs in the center bar.)
Micheal is understood to be the Archangel in charge of protecting Israel, Daniel 12:1. I believe there are Archangels assigned to each nation with angels under their command who also serve that nation. And each believer is assigned a guardian angel who protects them from lots of the consequences for the stupid things they do and many of the things trying to attack them that we're completely oblivious to, Psalm 91:11; Hebrews 1 which references Deuteronomy 32:43; Psalm 2:7; 104:4.
Angels are servants of God and when a person becomes a child of God by receiving Jesus as Lord of his life, they become that person's servants as well. We can ask God to send angels to protect our property and loved ones and to intervene in situations. There are many examples. George Washington served the English army before the revolution during the French and Indian War in the mid 1700's. In one battle he rode through the line of fire multiple times to deliver messages to commanders. Afterward when he took off his coat and hat, both had bullet holes in them, but he was unscathed. Later, a party of Indians met him in the forest and explained how they knew he was chosen by the Great Spirit: their best marksman had tried in vain to kill him and failed. During WWI the Germans failed to take advantage of a hole in the line of defense, which baffled American allies, but afterward during interviews they learned that the Germans had seen overwhelming forces protecting those holes and feared to attack them. Similar examples appear in the Bible, II Kings 6.
Angels ministered to Daniel in the lion's den, Daniel 6; angels tried to stop Balaam from making a mess of things for Israel, Numbers 22 and angels ministered to Jesus after He won the battle of wits with Satan, Matthew 4:11.
The Archangel Gabriel appears in Daniel 8:16; 9:21 and in Luke 1, seeming to function primarily as a messenger.
Michael and Gabriel are the only angels, except Lucifer who became Satan, who are named in the Bible.
Angels are described as "male," but Jesus said that they don't marry, Mark 12:25. It is my understanding that they are male, but cannot reproduce. In the passage in Daniel 10. Jesus appeared with two angels to discuss with Abraham the fate of the cities of Sodom and Gomorrah, Genesis 18. In Genesis 19 when the two angels arrive in Sodom the nasty men of the city find them so attractive they demand Lot send them outside his house so they can have sex with them, verse 5. Later, when God determines that He will in deed destroy the city angels make sure Lot and his family got out of town, Genesis 19.
There are hosts of angels, Psalm 148. Because of the allegorical story found in Revelation 12, we believe 1/3 of angels created at the time of Satan's rebellion joined him in his failed attempt to take God's throne away from Him.
Seraphim are only mentioned once, Isaiah 6.
The Nephilim, "the fallen ones," or "giants," are a mystery. Here's a pretty good discussion of Nephilim, http://www.gotquestions.org/Nephilim.html
But, though this author states that demons (or fallen angels) had sex with human women, we don't know this for certain. The passage in Genesis 6 could also be interpreted to refer to the "sons of God" as those who were of the lineage from which Jesus would eventually be born fooling around with women who had rejected God. We just don't know much about Nephilim.