What are angels? Evangelicals are so infatuated with angelic myths, that it's almost impossible to answer! From ancient times, to this very day, the movement of the stars, lightning strikes and earthquakes have been explained by angelic activity, but now all these events may be entirely explained by modern science. Nevertheless, today books on angels are still largely based on legends, personal experiences, and have run amok with all kinds of fictional traditions, that it's a temptation to completely disregard angelology entirely, and become agnostic to the existence of angels. So I was delighted to read Wolfhart Pannenberg's explanation of angels in his Systematic Theology Vol II., that presents a biblical angelology that is demythologized by modern science and free from the bondage of fictional angel traditions.
Angels are not Personal Spirits
Pannenberg builds his angelology upon Karl Barth's two hundred page analysis of angels in paragraph "§51 The Kingdom of Heaven, The Ambassadors of God and Their Opponents" of the Church Dogmatics Vol III.3 Pannenberg explains that (according to Barth), angels are not personal spirits, as popularly believed, and nothing positive may be said about the nature of angels according to the biblical data, and anything said about the nature of angels should be considered an "aberration." Angels are not personal creatures, like earthly creatures, and we only encounter angels when they are summoned to a specific event, and once this commissioned act is completed, their individuality disappears. Pannenberg (pace. Barth) compares the host of angels in heaven to a Spiritual "field", and individual angelic activity is best understood as forces or powers that are momentarily emitted from a field (and not as a personal spirit).
Pannenberg summarizes Barth's angelology as follows:
On this basis Barth advanced his thesis that angels, unlike earthly creatures, have no independent being (CD III/3, 480): "They do not exist and act independently or autonomously." . . . Barth viewed angels as "distinct creatures," yet not so clearly separate from one another as earthly individuals. They form the host of heaven. "Individual figures . . . exist only as they are specifically summoned and separated from the rest with a specific commission and in a specific relationship to the earthly history of salvation, disappearing again into the general body as soon as their work is accomplished." . . . If we understand the description of angels as spirits in analogy to what we have said about the Spirit as field, what is meant is not in the first instance a personal figure but a force. Thus the NT relates angels to such terms as "principalities" and "powers" (1 Pet 3:22; cf. 1 Cor 15:24; Eph 1:21; also Rom 8:28). All these powers are set under the dominion of the exalted Christ. 
The greatest difficulty besetting the traditional doctrine of angels lies in the idea that angels are personal spirits or subjects that serve God or, in the case of demons, that have turned against him. Nevertheless, if we remember that the use of personal predicates originates in the experience of being under the influence of not-wholly-explicable forces—an influence that works in a certain direction and thus shows itself to involve will--then the idea should not present us with insoluble problems. It is at any rate secondary to the experience. 
Pannenberg confesses that "Karl Barth's doctrine of angels in CD III/3 §51 is the most important discussion of the theme in modern theology"  and said that this understanding of angels as forces in a field, has "[t]o the astonishment of many observers, . . . produced in the 20th century theology a revival of the doctrine of angels and demons"  that has included many famous theologians such as Paul Tillich, Gerhard Ebeling, Paul Althaus, Hans-Georg Fritzsche, etc.
Angels and Science
The most helpful part of Pannenberg's angelology is his discussion of the works of angels in light of modern science. The Bible describes the movement of the stars, strikes of lightning, earthquakes, and other natural phenomena as the result of angelic activity, but we now know that these "acts of God" may be explained entirely with modern science. So how then do we understand these angelic acts?
In his Systematic Theology Vol II, in a section titled, "The Spirit of God and the Dynamic of Natural Occurrence", Pannenberg explains (pace. Barth) that the heavens and the earth correspond to the invisible and visible world (as described in the Nicene Creed cf. Col 1:16), such that what we know about the world is the visible earth, and what we cannot explain about the world is the invisible heavens. The purpose of angels, in this respect, is to help us understand the invisible world, in ancient times, but now that we are in the modern era, we are able to use science to understand the invisible motions of the natural world (without appealing to angels to explain natural phenomena).
In this section, Pannenberg responds to D.F. Strauss' criticism, that if angelic activity may be explained as modern science, then angels do not exist at all. Pannenberg summarizes D. F. Strauss as follows:
D. F. Strauss argued that the activity of angels in the world is in contradiction with modern science. Science does not view natural phenomena like thunder and lightning, earthquakes, pestilence, etc. as special acts of God but traces them to natural causes. This objection, however, is against the special activity of God in natural events no less than that of angels. It presupposes that the nexus of nature is a closed system, as in a mechanistic view of the universe. It assumes that theological statements about the activity of God or angels in cosmic events, or at least in specific events in nature, are simply explanations of natural processes that complete with scientific descriptions and the factors that these assert.
So are angels purely antiquated myth that are superseded by modern science? Pannenberg responds no, and says that we may still affirm the existence of angels, due to the contingency of the natural world. We may still understand stars, lightning and earthquake as natural events that may be explained purely by science, yet from another angel, we may understand those same natural events as angels or angelic activities. Nature is not a closed system (according to Pannenberg), so the ultimate cause of those events may still be understood as forces resulting from the angelic field. Angels are not personal spirits, but they are forces at work in the world, even if those forces may also be explained through modern science.
Pannenberg answers D.F. Strauss's objections to the existence of angels, and explains the relationship of angels to the natural sciences as follows:
If we allow, however, that scientific descriptions are not an exhaustive explanation of events and that the causal relation of events does not rule out but presupposes the contingency of individual events, and if we view the nexus of nature itself as a system that is open to contingency and not closed, then there need be no rivalry between scientific and theological statements. Both may well relate to the same events. Fundamentally, the angels of the biblical tradition are natural forces that from another angle might be the object of scientific descriptions. If we define forces like wind or fire or stars as angels of God, then we are relating them to God their Creator and to the human experience of being affected by them as servants of God or as demonic powers that oppose his will. Why should not natural forces in the forms in which we now known them be viewed as God's servants and messengers, i.e., as angels? 
In conclusion, Pannenberg provides us an angelology that allows us to affirm the existence of angels, without compromising our understand of modern science, or appealing to angelic myths. Knowing that angels are not "personal spirits" but forces that act from a spiritual field provides us a positive understanding of angels, that is biblical in nature, that still allows us to understand how the Spirit of God is at work in the world today, and provides us an ability to see natural phenomena (e.g. "acts of God") from a revelatory perspective (or secular parables).
[^Header Image Angel] By Giotto di Bondone, Public Domain, Link
[^Header Image Background] By Yintan - Own work, CC BY 4.0, Link
[^1] Pannenberg, Wolfhart. “Systematic Theology (Volume 2).” Systematic Theology (Volume 2), translated by Geoffrey W. Bromiley, Wm. B. Eerdmans Publishing Co., 2001, pp. 104–105. [parentheses with page numbers have been removed for readability]
[^2] Ibid. 106-7.
[^3] Ibid. 103.
[^4] Ibid. 105-6.
Related: angel, angelology, angels, D.F. Strauss, David Friedrich Strauss, Karl Barth, Myth, science, systematic theology, Wolfhart Pannenberg