The following article is quoted from the book 99 Answers to Questions About Angels, Demons & Spiritual Warfare by B.J. Oropeza.
The book, which presents a a balanced, level-headed and Biblical treatment of these subjects, is currently out of print. However, you may be able to obtain a second-hand copy via Amazon.com.
This material is copyrighted by B.J. Oropeza. It is quoted here by permission. [Details]
Perhaps the greatest speculations on the nature of angels came from a Dominican monk, Thomas Aquinas (1225-74), who earned the title Doctor Angelicus. Aquinas answered 118 questions about the character and attributes of angels and provided a basic definition of angels: “purely spiritual, intellectual and non-corporeal creatures, with ‘substances.’ 
Let’s break down this definition to note several aspects of the nature of angels.
- Angels are spirits
Like God, angels are spirits (invisible and immaterial essences) who are not limited by the physical constraints put on humans (Hebrews. 1:14; compare Job 4:15-16). 
For one thing, angels never die (Luke 20:36). Thomas Aquinas claims that angels are able to take on the physical appearance of eating, talking, and so forth, even though they are not actually fulfilling such activities (Summa Contra Gentiles 50:5; 51:3, cf. Tobit 12:19; Phlio Quaestines in Genesin 4:9′ Josephus Antiquities of the Jews 1.11.2)
If they are spirits, they probably do not have physical digestive systems. Nevertheless, angels can interact with the physical world. The angel at Christ’s resurrection had not problem removing the heavy stone that sealed Christ’s tomb (Matthew 28:2; Mark 16:3-4).
- Angels are superhuman beings
Angels are superhuman in the sense that they have greater abilities than humans. They can open prison doors to free captives (Acts 5:19; 12:5-11), they reveal messages from God (Acts 10:3-4; 23:9, 27:23), and they bring physical judgment on the wicked (Acts 12:23). In Genesis they blinded the men of Sodom who were trying to molest them.
In Revelation 7:1, John depicts four angels that hold the four winds of the earth. This perhaps implies a Jewish belief that angels have power over nature (2 Enoch 5:1).
We do not know, however, whether the angels perform superhuman feats by their own power or whether they are specially empowered by God for the occasion. Whatever the case, good angels act in harmony with the will of God.
- Angels are personal beings
Unlike earthquakes, tornadoes, radar and other impersonal forces, angels are persons. They are not merely God’s chesspieces or spiritual robots; they have intellect, emotion and will.
Regarding intellect, they have wisdom and can discern between good and evil (2 Samuel 14:17-20; 19:27). They long to understand the complete plan of God’s redemption (1 Peter 1:10-12); Ephesians 3:10).
Regarding emotion, they rejoice over God’s creation and over any sinner who repents (Job 38:7; Luke 15:7, 10). We might assume therefore that they grieve over those who reject the message of salvation (Pseudo-Philo 19.12-16) 
Regarding volution, they willfully choose to obey God’s word (Psalms 103:20; Revelation 22:8-9), although some who are called fallen angels have chosen to disobey God (Jude 6).
- Angels are holy beings
Angels are sometimes called “holy ones” (Daniel 4:13, 17; 1 Thessalonians 3:13; Jude 14; Revelation 14:10; 1QH 3.22, 4.25; 11.12; 1QM 1.10-11; 14.15-16).
Although they can clothe themselves with glory and splendor (Luke 2:9; 24:4-5) and they have access to heaven (Genesis 28:12; Luke 2:13-15; John 1:51), their holiness comes from God. Angels do not possess perfect holiness; they worship God alone as the absolute holy one (Job 4:18-19; 15:15) 
The seraphim angels cry “holy, holy, holy” before the throne of the Almighty (Isaiah 6:2-3; Revelation 4:8). They Jews understood God to be so holy that if the angels forgot to say “holy,” God would consume them with fire and create new ones (3 Enoch 40:3-4)!
- Angels are not gods
Angels are not minor deities like the ones in Greek mythology. Such a view of angels would amount to polytheism — belief in many gods.
The Bible declares that there is only one God (monotheism) and there there are no other gods but him (1 Corinthians 8:1-5; Galatians 4:8; Isaiah 41:10-11).
Angels are inferior to God and do not have God’s attributes of eternality, omnipotence (all-powerful), omniscience (all-knowing) and omnipresence (everywhere present) 
- This summarized definition of Aquinas’ view on angels comes from Karl Barth in Church Dogmatics (Edingburgh: T.amp T Clark, 1960), 3/2:391. Barth calls Aquinas’ work Summa Contra Gentiles “probably the greatest angelogue of all Church history.” However, he considers it a work of philosophy rather than theology, and he claims, “In its misguidedness we can compare it only with the foolish explanations which many modern theologians have given for their complete scepticism or indifference to the whole problem [of angels]” (3:391-92). Apparently Barth would blame Aquinas for the modernists’ mocking assertion that medieval theologians spent their time pursuing silly questions, such as, How many angels dance on the head of a pin?
- Hebrews 1:7 (“who maketh his angels spiritual, and his ministers a flame of fire,” KJV) is often used as a proof text supporting the spiritual nature angels. The best rendering of this text, however, is “He [God] makes his angels winds…” (compare Psalms 104:4). In the context of Hebrews 1, this passage contrasts the subordinate and transitory nature of angels (portrayed as “winds” and “fire” compare 2 Esdras 8:21; 2 Apocalypse of Baruch 21:6; 48:8) with the superior and permanent nature of Christ (Hebrews 1:4-6; 8:13). In one rabbinic tradition the angels declare, “God changes us every hour… sometimes he makes us fire, at other times wind” (Yalkut Shimeioni 2.11.3)
- Aquinas, on the other hand, claims that although angels can rejoice, they cannot weep. They cannot experience sorrow and pain because they are in a permanent state of heavenly bless (Summa Contra Gentiles 113:7)
- Some early church traditions speculated that the angels are perfected by the Holy Spirit (Basis Homilies 32:4)
- Thomas Aquinas argued that angels must always be at a respective point in time and only one angel can be at any one exact location at one time. Like other creatures, they must move about from one place to another (Summa Contra Gentiles 50:3; 42-52). The precise nature of angels in reference to space and time, however, is difficult to decipher. If angels are spirits, are they not extradimensional beings that are not subject to the laws of physics that apply to all human beings?
– Source: 99 Answers to Questions About Angels, Demons & Spiritual Warfare by B.J. Oropeza. © Copyright, B.J. Oropeza. Pages 19-21. Quoted at Apologetics Index by permission from the author. [Formatting notes]
This article is quoted from the book 99 Answers to Questions About Angels, Demons & Spiritual Warfare by B.J. Oropeza. InterVarsity Press (August 1997).
The book is currently out of print, and copyright has reverted to the author, B.J. Oropeza, who has kindly permitted us to publish this excerpt. [Copyright and linking information]
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