The function of Angels
Angels are created beings and they are ministering spirits (Heb. 1:13-14). They do not have natural human bodies, although they appeared in the form of men (Heb. 13:2).
Some angels (like seraphim) are created specifically for the purpose of ministering in the immediate presence of God (Isaiah 6:1-3). One of the functions of angels is to be part of the heavenly court. The heavenly host includes angels and archangels, which indicates a hierarchy, an order of authority within the angelic world.
Another function of angels is to serve as messengers. In fact, the Greek word for angel means “messenger.” The angel Gabriel was sent to announce the birth of John the Baptist and then to Mary to announce the birth of Jesus (cf. Luke 2:14).
Additionally, angels ministered to Jesus after He had endured forty days of temptation by Satan in the wilderness. When Jesus was arrested, He claimed that He had the authority to call upon legions of angels who could come and rescue Him (Matt. 26:53). Both His resurrection and ascension into heaven were heralded by the presence of angels. And when Christ returns, He will come with His angels in glory (Mark 8:38).
Satan and Demons
Satan and his fallen angels were originally created good and holy. Satan is a creature. He does not have the power of God. Yet he is more powerful and crafty than human beings. Because he is far weaker than God himself, anyone indwelt by the Holy Spirit does not have a fear of being possessed by a demon (1 John 4:4).
We are warned against the crafty power of Satan because we are no different than Peter, who in his arrogance assumed that he could withstand temptation and then went on to deny Jesus (Luke 22:31). Satan has the ability to appear as an angel of light (2 Cor. 11:14). “He will try to deceive us by coming to us not in an ugly state but as pious and pure, perhaps even quoting Scripture while causing us to go against the Word of God.”
Satan is the tempter, the deceiver, and the accuser. He delights to entice people to sin, even as he sought to cause Christ to fall during the wilderness temptation. He delights in accusing us of sin. His goal is to drive us to despair rather than to repentance. Satan accuses us of sin but simultaneously hides the remedy. He would have us destroy ourselves, whereas Christ calls us to forgiveness and redemption. The Scriptures tell us if we resist Satan, he will flee from us (James 4:7).
[Adapted from Everyone’s a Theologian by R.C. Sproul]