The 144,000 do not all live at the same time but live throughout the duration of the new dispensation. As the dragon directs his fury against the offspring of the woman generation after generation, the Lamb on Mount Zion preserves his redeemed generation after generation. Successive generations, then, learn this God-glorifying song as their antennae are tuned to heaven.
3 and they were singing a new song before the throne and before the four living creatures and before the elders. No one could learn that song except the 144,000 who had been redeemed from the earth.