Isaiah 21:9 “Look what’s coming! A charioteer, a team of horses. When questioned, he replies, ‘Babylon has fallen, fallen! All the idols of her gods lie shattered on the ground!’”
In contrast to those who are “sealed” by the beast, we see those who have been sealed by God! Whoever the 144,000 represent, they are completely and totally His. The fact that they are virgins may allude to that. Frequently in the Bible spiritual idolatry is likened to adultery: “They consult their wooden idols, and their diviner’s staff answers with an oracle. The wind of prostitution blows them astray; they commit spiritual adultery against their God” (Hosea 4:12). These are those God has redeemed, who sing a new song of salvation, and who follow the Lamb wherever He goes. They become an example of devotion for us to emulate.
Babylon may refer to Rome, or may simply refer to the ungodly kingdoms of the world. They are no match for God, and will one day be destroyed! They will drink of the cup of His wrath, but believers will be nourished by the water that flows from His throne (Revelation 22:1)!
Forever means forever in Revelation. We see that God exists forever (10:6), and the saints reign forever (22:5) Here the smoke from the torture of the ungodly goes up forever and ever in front of the holy angels and the Lamb (14:10-11). At the very least this shows that there are no second chances (Hebrews 9:27), but it also seems to indicate that whatever type of punishment they endure is conscious and eternal (Luke 16:19-31).
For contemplation: https://www.youtube.com/watch?v=oE85Edc6Q-A