Gretchen,
One fact you must learn and keep in mind in Biblical Studies is that the Bible contains a variety of book genre (kinds or types of books). We should not interpret historiography as poetry, or apocalyptic as narrative, or epistles as history. Therefore, the book of Revelation and its Greek language should primarily be interpreted in light of its usages and contexts, and so we ought to be careful not to mix it too inattentively with other NT books, such as Paul's letters or the Gospel of Mark. Revelation overwhelmingly uses the OT--especially Daniel, Isaiah, Zechariah) for its imagery and often quotes from the LXX (Septuagint / Greek OT) word-for-word. Clearly, the context of Revelation is the 90s CE (Roman Empire) during which John had a revelation from Jesus about things that were happening and that will happen in the future (however we each interpret all of this). Therefore, we should not mix Revelation too much with Mark and Paul. There are far more textual relationships between the Gospels and Paul than they have with Revelation. Revelation has far more explicit (black and white) textual relationships with LXX Daniel, Isaiah and other OT prophetic books.
Now, as Gina pointed out, angel = messenger and it's an umbrella term for any human or heavenly messenger depending on context (whatever precisely messenger can mean per context).
Also, in Mark and Paul, Ktisis is creation. We do not interpret words by ONLY using lexicons--and Strong's is outdated by the way. No scholar today uses Strong's. Everyone in scholarship uses HALOT (For Hebrew OT = Hebrew + Aramaic) and BDAG (for Greek and Hellenistic literature). Lexicons are not totally exhaustive, even the ones like BDAG that are exhaustive. And Lexicographers warn us about word fallacies that a lot of people make, which is to carry the meaning of a word entry in a lexicon and apply it however one sees fit in all other texts. It does not work that way.
Now, why some scholars have understood some of the angels in Revelation as pastors? I dont specialize in Revelation, but I do have a specialized commentary on Revelation that a lot of active, modern NT scholars have recognized for being one of the best elaborated commentaries on Revelation so far. Here's what Gregory Beale says on this matter:
Instead of “to the angel of the (τῆς) church in Ephesus,” some
manuscripts read “to the angel of the church who (τω) [is] in Ephesus”
(A C 1854 pc), which locates the angel actually in the church. This
variant occurs in the introduction to each letter (2:8, 12, 18; 3:1)
except those to Philadelphia and Laodicea (3:7, 14). Perhaps the
change was motivated by an attempt to identify the “angel” as a
bishop, pastor, or elder in the church. The genitive reading is more
probable because of external manuscript evidence and because it places
the angel in a position over the church (as its guardian angel). If
the “angel” is understood as a human letter carrier (like Tychicus,
Eph. 6:21–22; Col. 4:7–9), then an objective genitive might be in view
(“to the church”). In 2:3 codex Sinaiticus (א*) reads “you also have
all afflictions” (θλιψεις πασας), which may reflect an early
interpretation affirming that the trials at Ephesus included more than
mere internal strife but perhaps also external persecution (see this
use of θλίψις [“tribulation”] in 1:9; 2:9, 10, 22; 7:14).
G. K. Beale, The Book of Revelation: A Commentary on the Greek Text
(New International Greek Testament Commentary; Grand Rapids, MI;
Carlisle, Cumbria: W.B. Eerdmans; Paternoster Press, 1999), 230.
But, Beale doesn't think that the "pastors" view is the best view. Instead, he prefers the heavenly beings view. I cannot paste the whole section of his commentary, it would be too lengthy for this forum, but I'll be selective:
Why are the churches addressed through their angelic representatives
in the letters, especially since it does not seem logical to blame and
reproach angels for the sins of the churches? The initial answer to
this is that inherent to the concept of corporate representation is
the representative’s accountability for the group and the group’s
accountability for the actions of the representative. So there is some
sense in which the angels are accountable (e.g., responsibility of
oversight) for the churches, yet the churches also benefit from the
position of the angels. The fuller reason for addressing the churches
through their representative angels is to remind the churches that
already a dimension of their existence is heavenly, that their real
home is not with the unbelieving “earth dwellers” (cf. “earth
dwellers” in 3:10 and passim), and that they have heavenly help and
protection in their struggle not to be conformed to their pagan
environment......
......The conclusion that ἄγγελοι in 1:20b refer to heavenly angels who
represent the church is supported further by the following two broad
considerations. (1) Stars as metaphorical for both saints and angels
in the OT and Judaism. (2) Angels as corporate representatives of
saints in the OT, NT, and Jewish writings.....
......In this regard, it is not too speculative to view the number of “seven
stars” as having arisen also in part from the “seven lamps” of
Zechariah 4, since the two symbols have been directly related in
Revelation 1:20 (λαμπρότης [“brightness”] in Dan. 12:3 [Theod.] and
λαμπάδιον [“lampstand”] in Zech. 4:2–3 may have served as further
attracting factors, in addition to the “stone” associations between
Zechariah 4 and the Daniel “Son of man”; see below). Perhaps since the
one lampstand from Zechariah 4 was increased to seven in order to
indicate universality, the stars of Daniel 12 may have undergone the
same hermeneutical development. A similar phenomenon is traceable in 1
En. 90:20–25, where “seven white ones” (= angels) and seventy “stars”
(= angels) are based on the context of Daniel (Dan. 7:10; 9:2, 24;
12:1–3; cf. also 1 En. 21:3, where seven stars are equivalent to seven
angels). This evidence suggests that these stars are heavenly angelic
beings (see 1 En. 86:1–3 and 88:1, where stars also symbolize angels)....
....For early Jewish symbolic identification of the seven lamps in the
temple with the seven planets see Josephus, Ant. 3.145; War 5.217;
Philo, Quis Rerum Divinarum Heres 45.221–25; Vita Mosis 2.102–5;
Quaestiones in Exodum 2.73–81; Targ. Pal. Exod. 40:4. Midr. Rab. Num.
12.13 equates the seven lamps with the “lights of the firmament of the heaven.”
G. K. Beale, The Book of Revelation: A Commentary on the Greek Text
(New International Greek Testament Commentary; Grand Rapids, MI;
Carlisle, Cumbria: W.B. Eerdmans; Paternoster Press, 1999)
So the "pastors" view seems to have arisen even by some copyists of the NT as far as we can tell in some manuscript variants of Revelation and how one may read and understand the Greek text today in light of the fact a messenger could be a human being and could have been a representative of a local church. But, as Beale and others prefer, it most likely points to heavenly beings--in this particular case, sort of guardian angels.
Now, your post asks : "Are angels creatures (Mark 16:15) and can they repent (Rev 2:5 and Rom 8:21)"
Well, heavenly beings can be called creatures in the OT and NT. I recall the Cherubim in Ezekiel are living creatures, but the context is clearly heavenly. Also, John in Revelation 4.6 uses "living creatures" to refer to these heavenly beings as Revelation also uses the LXX of Ezekiel. The Ktisis in Mark and Paul refer to the creation (humankind).
I dont see anywhere in the entire canonical literature (OT and NT -- with some allusions to 1 Enoch) that heavenly angels can repent from their sins. Only the contrary is found in Isaiah 24:21, Psalm 82 and 1 Peter 3.18-22, 2 Peter 2.4, Jude 5-8.
