Recovery,
As requested, a discussion on the Great Crowd and the identity of the Other Sheep.
First question: Where are the Great Crowd rendering sacred service day and night?
The proper exegesis of this question within the symbolic language of this passage makes or breaks any hermeneutical interpretation built on top of that foundation. So, first, we must get the foundation right.
A very good tool for this is Blue Letter Bible. For instance, please look at Revelation 7:15, broken down to the Koine.
http://www.blueletterbible.org/Bible.cfm?b=Rev&c=7&v=15&t=YLT#conc/15
First, we noticed the Great Crowd renders service. The word is latreuo , which means:
1) to serve for hire
2) to serve, minister to, either to the gods or men and used alike of slaves and freemen
a) in the NT, to render religious service or homage, to worship
b)to perform sacred services, to offer gifts, to worship God in the observance of the rites instituted for his worship
1) of priests, to officiate, to discharge the sacred office
WHERE does the Great Crowd render sacred service? In the naos, which was "used of the temple at Jerusalem, but only of the sacred edifice (or sanctuary) itself, consisting of the Holy place and the Holy of Holies (in classical Greek it is used of the sanctuary or cell of the temple, where the image of the god was placed which is distinguished from the whole enclosure)"
The word naos which consisted of the Holy and Most Holy, is distinguished from word hieron. For instance, at Matthew 21:12, Jesus throws the moneychangers from the hieron (temple grounds), not the naos (the sanctuary).
About the word hieron we read:
The word "temple" in the NT, with respect to the temple at Jerusalem, often referred to the entire precinct which included the sanctuary, courts, and other buildings. The temple of Jerusalem consisted of the whole of the sacred enclosure, embracing the entire aggregate of buildings, balconies, porticos, courts (that is that of the men of Israel, that of the women, and that of the priests), belonging to the temple; the latter designates the sacred edifice properly so called, consisting of two parts, the "sanctuary" or "Holy Place" (which no one except the priests was allowed to enter), and the "Holy of Holies" or "the most holy place" (which was entered only on the great day of atonement by the high priest alone). Also there were the courts where Jesus or the apostles taught or encountered adversaries, and the like, "in the temple"; also the courts of the temple, of the Gentiles, out of which Jesus drove the buyers and sellers and the money changers, court of the women.
The word hieron is not found in the book of Revelation. But is it possible that the great crowd are in the courtyards? To clarify the word naos in Revelation, we need to turn to Revelation 11:2 and look at the Koine Greek.
http://www.blueletterbible.org/Bible.cfm?b=Rev&c=11&v=2&t=YLT#conc/2
Notice in this vision, the aule(court or courtyard) is distinguished from the naos, in fact, the courtyard is outside the Temple Sanctuary.
Conclusion: The Great Crowd cannot be in the courtyard, since they are in the the Temple Sanctuary, the Holy Place. If they rendering sacred service in the Holy Place, they carry out a priestly duty. If they are carrying out a priestly duty, they cannot be a secondary class of Christians with a lesser hope. This is in harmony with 1 Peter 2:5, which says, "And you yourselves, as living stones, are built up, a spiritual house, a holy priesthood, to offer up spiritual sacrifices acceptable to God through Jesus Christ."