'The first resurrection,' mentioned in Revelation 20:5, 6, does not mean a first resurrection, but the essence and primary part of resurrection, which is salvation and eternal life. There is only one resurrection to life. A second does not happen, and is not mentioned anywhere in the Bible.

(References: Apocalypse Explained 6; Apocalypse Revealed 851; Revelation 20:5-6)

850. 20:5 But the rest of the dead did not live again until the thousand years were completed. This symbolically means that besides these just described, no others were raised into heaven until after the dragon was set loose and they were then tried and examined to discover their character.

The rest of the dead symbolize people who were rejected by those caught up in faith alone because they worshiped the Lord and lived in accordance with His commandments, but who had not yet been tried and examined to discover their character. That these are the people symbolized by the dead here may be seen in no. 847 above. For after their departure from the world, all people first come into the world of spirits, which is midway between heaven and hell, and there they are tried and examined and in this way prepared, the evil for hell and the good for heaven. It is said of these that they did not live again, that is, that they were not yet so conjoined with the Lord and affiliated with angels in heaven as the first people were.

That many of these were afterward saved is apparent from verses 12 to 15 in this chapter, where we are told that the Book of Life was also opened, and anyone not found written in the Book of Life was cast into the lake of fire.