These are they which were not defiled with women; for they are virgins. These are they which follow the Lamb whithersoever he goeth. These were redeemed from among men, being the firstfruits unto God and to the Lamb.
These people remained pure and didn't have relationships with women because they stayed that way. They stick close to the Lamb (Jesus) wherever He goes. They were saved from all of humanity and are the first ones chosen by God and Jesus.