These elders are spirit beings created by God to be His wise and intelligent counselors. They were created before the physical creation, along with cherubim (Gabriel, Michael and Lucifer are the only three mentioned in the Bible), the seraphim, the four living creatures and the billions of other angels that serve God.
There are some who falsely claim that the 24 elders are taken from saved mortals. This erroneous teaching comes from a mistranslation of Revelation 5:8-10, which states, “And when He had taken the book, the four beasts and four and twenty elders fell down before the Lamb, having everyone of them harps, and golden vials full of odors, which are the prayers of the saints. And they sung a new song, saying, You are worthy to take the book, and to open the seals thereof: for You were slain, and have redeemed us [them] to God by the blood out of every kindred, and tongue, and people, and nation; And have made us [them] unto our God kings and priests: and we [they] shall reign on the earth.” The italicized words should be replaced by the words in brackets. See the Revised Standard Version, and also the margin of the New King James Version.
It would be impossible for these 24 elders to be resurrected saints. John 3:13 states, “And no man has ascended up to heaven, but He that came down from heaven, even the Son of Man which is in heaven.” When Christ returns to this earth, those who are His will be given immortality (I Cor. 15:23). Not before!
These 24 elders rule with God in heaven and have been given an advisory role to Him. The resurrected saints will rule on the earth (Rev. 20:4).