Those 144,000 are the people who are spiritually pure, like virgins are morally pure. They have not ◄defiled themselves/made themselves impure► [MET] by worshipping any false god. They are the ones who accompany Jesus, the one who is like a lamb, wherever he goes. They represent all those whom he has redeemed/bought for God from among the people of earth, in order that he might offer them to God and to himself.