I would like, in this post, to look at Revelation 7, particularly at the two groups mentioned: the 144,000 and the great multitude. Many, if not most, Reformed commentators (see Beale especially) have argued that these are the same groups of people. It must be admitted from the start that this is a very respectable position with a long pedigree. Nor can the difference between a numbered group and an innumerable group be attested in support of the position that there are two different groups.
The number 144,000 is a symbolic number. This is obvious from several facts. That God would only seal some and not others implies two distinct classes of Christians, something which the rest of the New Testament takes quite some pains to deny. Whatever group the 144,000 represents, it cannot be only part of a group of Christians.
Incidentally, as the commentator Wilmshurst (in the Welwyn series) points out, the Jehovah’s Witnesses interpretation makes this mistake and several others. The JW interpretation states that the 144,000 is a literal group of people that are to be in heaven around the throne room of God, and that the rest of the “good” people will have a decent life here on earth. Both groups are interpreted eschatologically in JW theology. However, the text makes it quite explicit that it is the great multitude who are around the throne of God in heaven, whereas the 144,000 are sealed here on earth to prevent them from receiving ultimate harm from the seals (see the flow of context from chapter 6). So the JW’s get the location of each group wrong. They also interpret the number literally, when it should be interpreted symbolically as 12 X 12 X 1000 (possibly the OT saints plus the NT saints times the number of perfection, implying the entirety).
We are more on the right track when we remember that census numbers were usually taken for military purposes. The 144,000 is a fighting group of people. This is confirmed when we look at chapter 14, the other time the 144,000 make their appearance. They were those who had not defiled themselves with women. Again, this is usually interpreted differently to point to their spiritual purity (and, no doubt, that is included). However, while fighting, Israelite men were to keep themselves from women. The indications are that the 144,000 is a fighting group.
However, they are not Israelites, contrary to the appearances of verses 5-8. For one thing, there wasn’t a Northern kingdom at the time John was writing. Secondly, the order of names is very curious (including Joseph and Manassah, but not Ephraim, and completely excluding Dan; as well as putting Judah first, and the sons of the concubines are fronted over some of the other sons of Leah, which would seem to indicate Gentile inclusion, as several commentators note). The only other group they could be is the church.
The innumerable multitude are standing around the throne room (and hence do not need the seal, since they are already safe). They hold palm fronds (v. 9), which is a symbol of military victory. They have their white robes that have been washed in the blood of the Lamb (v. 13). They are out of the tribulation (v. 14).
The upshot of the whole here is to point to the logical conclusion: the 144,000 symbolizes the church militant; and the innumerable multitude symbolizes the church triumphant. This avoids the problem of seeing the 144,000 as part of a group (in the sense that the entire church militant is sealed, not part of it: I am not advocating a denial of the distinction between the church militant and the church triumphant). The indications of the military nature of the 144,000 are given full scope, as well as the triumphant nature of the innumerable multitude. This is roughly the same conclusion to which Dennis Johnson arrives, although I have fleshed out the arguments a bit more than he did.