On Palm Sunday Jesus marched into Jerusalem on a donkey before his death. This shows that Jesus conquers not through military might but weakness, not the power of a lion but the weakness of a lamb (Rev 5:5–6). Not only does Jesus conquer in this way, but the church follows the Lamb wherever he goes (Rev 14:4). Revelation 7 develops the image of Rev 5:5–6 and applies it to the church as a whole; the army led by Judah (Rev 7:1–8; cf. 5:5) is the multitude of worshipers of the Lamb (7:9–17; cf. 5:6). As a result Revelation 7:9 is less a worship service and more of a post-battle victory song. We see that our diverse army is assured victory through perseverance which is rewarded.
First we see a diverse army (Rev 7:1–9). A census of young males (7:4) typically suggests military preparation, with a sealing suggesting God’s protection (7:3). They are led by the tribe of Judah (7:5), because this is the army of the Lion of Judah (5:5) whose power is expressed through the Lamb that was slain (5:6; cf. 7:9). Oddly, the order of the tribes of Israel begins with Judah, neglects Dan and adds Manasseh, and its order places the sons of the concubines before the sons of Jacob’s wives (7:5–8). And this mighty army of the Lion of Judah is interpreted as the multiethnic, multilingual multitude before the Lamb (7:9), just as the Lion of Judah is interpreted as the Lamb that was slain (5:5–6). God’s army comes from every background, every nation, and every tongue; no one is excluded from participation because of their ability or background.
Yet though we step into battle, our diverse army is assured victory because of the power of our God (7:10–12). The victory cry will go up, “Salvation belongs to our God who sits on the throne, and to the Lamb” (7:10)! This victory is not because of the greatness of ourselves but the power of our God on the throne. And the angels who stand around the throne and see every detail of what God is doing give glory and honor and power to God for that victory (7:12). Therefore, this victory cry reminds us that God is the assurance of our victory.
Although our victory is assured, this victory happens through perseverance, made possible by the sacrifice of the Lamb (7:13–14). This army is clothed with white robes, the reward of those who persevere without compromise in the face of corruption (3:4–5). Now a robe is white because it has avoided dirt or been washed; purity is not simply the avoiding of evil but also perseverance in the face of evil. Just as robes must be washed after battle, so God’s people are pure because they have persevered and overcome in their battle with evil. This is possible not because of their perfection but their purification; our robes are made…white in the blood of the Lamb (7:14). Our perseverance is made possible because of what Jesus Christ has done on the cross for us.
While the battle will take its toll, we know that perseverance is rewarded (7:15–17). While the battle rages there will be a cost. We look forward that in the shelter of his presence (7:15) we find satisfaction (without hunger or thirst), protection (from the sun and heat; 7:16) and restoration from living water and tears wiped away (7:17). This means that the battle may be costly as we are exposed to hunger, thirst, heat, and anguished tears, but we look forward to when these pains will be rewarded.
So rise up church. We are called to be a church ready for battle. God does not call us to comfort but he calls us to victory. Yet our diverse army is assured victory through perseverance which is rewarded.
 Revelation 7:9 is often used to argue for a multiethnic church on earth. Since Rev 7:9 pictures a heavenly worship service with people from every nation, therefore we ought to have our earthly worship ought to reflect that same reality. Yet the picture is more of a post battle victory song! The dominant imagery is militaristic: censuses were typically taken to prepare people for war (Rev 7:4), palm branches is peace after war (7:9), and washing robes happens after battle (7:14).