The vision of this chapter opens with “a Lamb stood on mount Zion”. In chapter 13:11, the false lamb was seen, who “spoke as a dragon”. Here, in contrast, we see the Lamb of God, the same Lamb as in Revelation 5:6,7. In chapter 5 it is clear that the Lamb is Christ who took the book with seven-sealed book. Here and in Hebrews 12:22 are the only verses in the New Testament where the phrase ‘on mount Zion’ occurs. It is the same as “Jerusalem above” of Galatians 4:26. Hebrews 12:22 defines Mount Zion as the heavenly Jerusalem. Mount Zion is symbolic of the city of the great King, the seat of the worship of God in Jerusalem, and is used as a symbol of the true Church (Psalm 125:1,2). The saints who have entered into the covenant of Christ are said to have come, not to the mount that could not be touched, but to Mount Zion, the city of the living God, the heavenly Jerusalem. It is there used for the church of the saints, and such is its meaning in this passage
The Church of true believers are also marked in their foreheads (v.1), yet this is not a literal mark. The 144,000 (v.1-4) is symbolic of the believers who stand against the Satanic evil of the Papacy and its forces. In chapter 7:4, the same number are spoken of as sealed from the twelve tribes of Israel. It means there, a great, indefinite number. Here, I take that the meaning is the same. It is a great multitude, a round number, who are associated with the Lamb. (Alternate views of what the 144,000 represents include that it represents some 144,000 Jewish believers, or, a chosen 144,000 believers from the Christian church).
In verse 4 there is reference to those “not defiled with women”. This means those who refuse sinful intercourse with the world. Spiritual adultery or fornication is being wedded to the world and partaking of its sins. The expression “they are virgins” is symbolic that their lives are not defiled by the world. See 2 Corinthians 11:2; Hosea 2:19,20.
The believers were found to be without fault, because they are forgiven, and their sins are washed away (v.5). Then John saw “another angel fly”, which is symbolic of the true gospel being rapidly preached throughout the world to every nation and language group (v.6). The angel (v.6,7) means God’s Holy Spirit is the agency whereby this message is preached to the world. Since the Reformation the preaching of the gospel to the world has expanded quickly and is continuing to this time. This does seem to put us now towards the very end of world history (but who can say?).