REV 14:3

3 The 144,000 people were singing a new song [while they stood] in front of the throne, in front of the four living [creatures], and in front of the elders. Only the 144,000 [people], the ones who have been {whom [the one who is like a lamb] has} redeemed/bought from among the people on the earth, could learn that song. No one else could learn the song [that they sang].