Lets go over the OP passage again:
22 But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, and to myriads of angels,
23 to the general assembly and church of the firstborn who are enrolled in heaven, and to God, the Judge of all, and to the spirits of
the righteous made perfect,
1) Where are we? In the heavenly Jerusalem, where the church of the first born is located made up of the
"spirits of the righteous made perfect."
2) What is the status of those spirits? They have been made perfect, thus put in Christ, regenerated, and born anew. These spirits have been enrolled in heaven. Thus they were not enrolled before they were made perfect, before being born anew, before being put in Christ, as part of the bride and body of Christ. OTOH,
they have been made alive together with Christ, and therefore belong in the Lamb's book of life.
3) Some claim the spirits might have been enrolled before they became members of the church of the firstborn. But that is an absurd and unnatural interpretation. When people are enrolled in something, they are members of that something, a group, church or whatever.
4) Why have so many objected to this mainstream view of the passage? Either they want to claim the OT book of the living (
Psalms 69:28) is the Lamb's book of life (
Revelation 3:5, 21:27). or they want to claim names were written in the Lamb's book of life before the foundation of the world, specifically precluded by
Revelation 13:8 and 17:8.