Here is the next post in my theology in bullet points series. The previous one is here.
There are both good and evil spiritual beings at work in the world. Before the Enlightenment of the 1600s and 1700s, belief in invisible beings like angels and demons was part of everyone's view of the world. They remain part of common Christian belief today.
The original creed that came out of the Council of Nicaea in AD325 already made a point of saying that God was the "maker of all things visible and invisible." The things invisible here refer not only to the fact that God created the very matter from which the world is created but also to indicate that God created angels, Satan, and demons. Nothing that exists is uncreated, but God has made everything that is.
1. Certain parts of the New Testament make it a point of showing that Christ is superior to all spiritual powers as well. The so called hymn in Colossians emphatically indicates that Christ created all "thrones or powers or rulers or authorities" (1:16). Here the hymn has heavenly rather than earthly authorities in view. Christ is the firstborn over all creation (1:15), including all spiritual powers. Ephesians 1:21 puts it this way, Christ is "far above all rule and authority, power and dominion, and every name that is invoked, not only in the present age but also in the one to come."
The sermon of Hebrews in the New Testament begins with a celebration of Christ's enthronement over all the creation. He is a Son while the angels are merely servants (e.g., 1:5-14). It is hard to know exactly what might have inspired such a hymnic exaltation of Christ in relation to the angels. Did some think that Christ was merely an angel? Did some have too exalted a view of the angels?
Whatever the precise cause, Hebrews makes it clear that Jesus took on human blood and flesh (2:14). He took on the flesh of Abraham's descendants, not the angels (2:16-17). The angels are just "ministering spirits" (1:14), but Christ and humanity are destined to rule in the coming kingdom (2:5).
Most Jews at the time of Christ believed in the existence of angels. The only group that may not have was the Sadducees, but this claim is based solely on a questionable interpretation of Acts 23:8.  It seems more likely that even the Sadducees believed in the existence of angels.
Angels do not play a huge role in the Old Testament, but they are present even in Genesis (e.g., Gen. 19:1). Of special interest is the Angel of the Lord, who is so closely associated with God that more than one text floats back and forth between saying that the Angel is speaking/present and saying that God is speaking/present (e.g., Exod. 3:2; Zech. 3:1-2). Some would like to equate this Angel with Jesus, although originally it was probably more an instance of this messenger of God fully representing God. The word "angel" in both Greek and Hebrew means "messenger."
In the latest parts of the Old Testament, we begin to hear names of angels. The angel Michael appears only in Daniel (Dan. 10:13, 21; 12:1) and appears to be the leader of God's angelic armies, fighting the powers associated with other nations.  Michael is also mentioned in the New Testament in Jude 9 and Revelation 12:7.
The angel Gabriel is also mentioned four times in the Bible, also starting in Daniel (8:16; 9:21). He serves a role of bringing messages from God to individuals on the earth. So it is no surprise that the New Testament gives his name as the one who brought the announcement to Mary that she would give birth to the Messiah (Luke 1:19, 26). We also hear of other names in Jewish literature (e.g., Raphael), but none of these have made it into the (Protestant) biblical texts. 
2. Christians generally view Satan as the arch-angelic enemy of God, the most powerful of all evil beings. (As we will argue in a later article, no being is intrinsically evil. Rather, evil is an adjective used to describe a certain kind of intention in relation to the choices a person makes.) Like the "man of lawlessness" described in 2 Thessalonians 2:4, Satan is opposed to everything that is associated with God. He is "that ancient serpent, who is called the Devil and Satan, the deceiver of the whole world" (Rev. 12:9).
Revelation here identifies Satan as the serpent in the Garden of Eden. This was a development in understanding that took place between the Old and the New Testaments. It is first attested in a Jewish writing from around the first century BC called The Life of Adam and Eve and is nowhere attested in the Old Testament itself. Revelation further identifies him as a dragon who swept a third of the stars from heaven (12:4), often interpreted to mean that Satan led a heavenly rebellion against God that resulted in a third of the angels falling from heaven.
We should point out how much of this interpretation is traditional rather than clearly biblical. Many common Christian thoughts on Satan are a matter of Christian tradition piecing together interpretations of obscure verses here and there, often reading those verses out of context. That does not mean that Christian tradition is wrong on its conclusions, since God gets the Church where he wants it to go. However, it may mean that there is more room for debate on these matters than some other common beliefs.
For example, Isaiah 14 in context does not mention Satan. This passage was clearly about the king of Babylon (cf. Isa. 14:4) and had to do with his eventual "meteoric" fall from power. In context, language of the morning star falling from the sky (14:12) was clearly poetic language that compared the fall of Babylon's power to something like the day star falling to the earth. Nowhere else is "Lucifer" (morning star) used of Satan in the Bible and in fact Jesus is called the morning star in Revelation 22:16.
Similarly, when Luke talks about Satan falling from heaven (Luke 10:18, or "from the sky"), it is in the context of the disciples casting out demons. In context, Jesus is not talking about some event that happened at the beginning of time but to something that was happening as a result of his ministry. Every demon Jesus cast out was a sign that the kingdom of God was arriving (Luke 11:20). Similarly, in Revelation 12:9, the dragon is cast to the earth as part of salvation.
In the Jewish view of the world at the time of the New Testament, evil powers were sometimes thought to inhabit the lowest region of heaven.  The Devil is thus the "ruler of the kingdom of the air, the spirit who is now at work in those who are disobedient" (Eph. 2:2). Hebrews 2:14 calls the Devil the one who has the power of death and sees Christ's death as the defeat of his power.
Again, we may find traces of less than fully developed understandings of Satan and of fallen angels in more obscure parts of Scripture. 1 Peter, 2 Peter, and Jude speak of fallen angels associated with the Flood who are "kept in darkness, bound with everlasting chains for judgment on the great Day" (Jude 6; cf. 1 Pet. 3:19-20; 2 Pet. 2:4). These comments seem to allude to Jewish traditions involving Enoch that understood the "sons of God" in Genesis 6:2 to be fallen angels. 
Similarly, Satan in Job is not yet said to be a fallen angel but his job seems rather to test God's servants to see if they will remain faithful. Arguably the three Old Testament texts that mention the accuser, Satan, all come from the period after Israel returned from exile (Job. 1 Chronicles, and Zechariah). Rather than God directly tempting or provoking evil, Satan is now understood to be a direct cause, with God's permission.
Despite the path to get there, common Christian understanding is generally that Satan is a fallen angel, one of the heavenly creations of God. As with the rest of the creation, God created him good but gave him and the other angels the same free will that he gave to Adam and humanity. He has chosen instead to rebel against God. His choice and the choice of the angels was made with such a height of knowledge that their choice was definitive. They would never repent even if given the opportunity.
Demons are fallen angels who similarly provoke evil on the earth. Jesus' earthly ministry already signaled their eventual defeat, and Jesus' death finalized it. In the meantime, they continue to wage war against the saints on earth and to provoke evil among those without the Spirit of God.
3. The distinction between natural and supernatural was a by-product of the rise of the Scientific Age in the 1600s. The "natural" came to refer to nature operating according to the laws of nature. The "supernatural" thus referred to the engagement of powers that did not operate according to the laws of nature.
Can angels and demons circumvent the laws of nature? It would seem so, at least to the extent that we understand them. In that sense, we might refer to them as supernatural in that their actions cannot be accounted for on the basis of the laws of physics as we understand them. However, from another perspective, they are part of the creation, personal agents who make choices and cause things to happen. Perhaps it would be more accurate to think that they represent a bigger perspective on nature than we are currently able to understand.
There are other obscure references to angels that seem too infrequent to build a thoroughgoing doctrine from. For example, Jesus speaks of the angels of children appearing before his face (Matt. 18:10). This is where we get the idea of children having guardian angels, but it is one of the only places in Scripture where such a comment is made.
Similarly, when some early Christians thought Peter was dead and yet knocking at the door, they wondered if it might be his angel (Acts 12:15). There is thus the possibility that some early Christians thought of us taking on a certain angelic form in the time between our death and resurrection.  Even Jesus suggests that in the resurrection we are like the angels (e.g., Mark 12:25).
But, again, these are relatively obscure comments in Scripture. The common Christian belief is not that we will become angels at death. The angels are "ministering spirits sent to serve those who will inherit salvation" (Heb. 1:14). But in our transformed, resurrected state, we will be greater than them, like the humanity of Jesus became greater than them in resurrection. They will be there around the eternal throne in worship with us (e.g., Heb. 12:22), but we will be there as kings and queens, not as servants.
There are good and evil spiritual beings at work in the world. The evil ones are destined for destruction, while we will worship alongside the good ones forever.
Next Sunday: C5. Human beings were created in the image of God.
 There is a tendency among many to see the Sadducees as ancient versions of modern liberals and anti-supernaturalists. But this is an anachronistic reading, an all too common and predictable imposition of modern issues on ancient individuals. In some respects, the Sadducees were more conservative than the Pharisees (for example, in their view of the afterlife--resurrection belief is not at all common in the Old Testament).
 In earlier parts of the Old Testament, these are the gods of the other nations. See, for example, Deuteronomy 32:8 in the New Revised Standard Version.
 Raphael appears throughout the book of Tobit, which is in the Catholic and Orthodox Bibles.
 See in particular a Jewish writing called the Testament of Levi.
 See especially 1 Enoch, which saw the origins of demons in the evil spirits produced when the giant offspring of angels and human women were killed.
 See N. T. Wright, The Resurrection of the Son of God (Philadelphia: Fortress, 2003), 134.