That is as true as the Gospel itself. Please take note of the CURRENT occupants of the New Jerusalem which is in Heaven (Heb 12:22-24):
But ye are come [spiritually in the present tense] unto mount Sion, and unto the city of the living God, the heavenly Jerusalem, and
[1] to an innumerable company of angels
[2] To the general assembly and Church of the firstborn, which are written in heaven [NT saints who have passed on]
[3] and to God the Judge of all,
[4] and to the spirits of just men made perfect, [OT saints who had passed on]
[5] And to Jesus the Mediator of the New Covenant,
[6] and to the blood of sprinkling, that speaketh better things than that of Abel.
Please note items 2 and 4. All the NT and OT saints who have passed on are now in Heaven with God, Christ, all the angels, as well as the blood of Christ sprinkled on the Mercy Seat. Why? Because OUR CITIZENSHIP IS IN HEAVEN.