12:22 mount Sion. In contrast to the frightening scene at Sinai is the wonderful glimpse of the heavenly Zion (Hebrews 12:22-24). This assemblage is now gathered in heaven, but will all become a glorious reality on earth when the “heavenly Jerusalem” descends out of heaven to the new earth (Revelation 21:2-7).
12:22 innumerable company of angels. Even though a third of God’s created angels followed Satan in his rebellion (Revelation 12:3,4), there still remains an innumerable host of heaven in the faithful angels, presumably associated with the innumerable starry hosts of heaven (Jeremiah 33:22).
12:23 church of the firstborn. The “church of the firstborn” will have all Christians of all times as its members. It will have its first full “assembly” in the future age, but presumably does meet on occasion even now, with the “spirits of [justified] men made perfect” coming together for fellowship and testimony.