The symbolism of beast is explained in Revelation 17 (WEB):
(9) Here is the mind that has wisdom. The seven heads are seven mountains on which the woman sits.
(10) They are seven kings. Five have fallen, the one is, the other has not yet come. When he comes, he must continue a little while.
(11) The beast that was, and is not, is himself also an eighth, and is of the seven; and he goes to destruction.
(12) The ten horns that you saw are ten kings who have received no kingdom as yet, but they receive authority as kings, with the beast, for one hour.
(13) These have one mind, and they give their power and authority to the beast.
(14) These will war against the Lamb, and the Lamb will overcome them, for he is Lord of lords, and King of kings, and those who are with him are called chosen and faithful.”
(15) He said to me, “The waters which you saw, where the prostitute sits, are peoples, multitudes, nations, and languages.
(16) The ten horns which you saw, and the beast, these will hate the prostitute, will make her desolate, will strip her naked, will eat her flesh, and will burn her utterly with fire.
(17) For God has put in their hearts to do what he has in mind, to be of one mind, and to give their kingdom to the beast, until the words of God should be accomplished.
(18) The woman whom you saw is the great city {Rome}, which reigns over the kings of the earth.”
It is symbolic of events that happen during the Gospel age (including the time of that John was given the revelation), not of events during the Great Tribulation.
Therefore those described as not having worshiped the beast (the second beast), nor received it's name or mark (I believe it's referring to Islam), could have lived at any time during the last 2,000 years.
So they probably represent Christians that have lived during the Gospel Age, which ends at the rapture (first resurrection) - before the Great Tribulation.
A more accurate and literal translation is "they lived", not that they "came to life".
If they are meant to be the great multitude mentioned in Revelation 7, who came through the great tribulation, then "they are before the throne of God, they
serve him day and night in his temple" (verse 15), whereas the resurrected Church sit on thrones and are priests of God and of Jesus, and will reign with Jesus for one thousand years (Revelation 20:4,6). The resurrected Church will be immortal, whereas the great multitude are not, which is why Jesus "leads them to springs of life-giving waters" (Revelation 7:17), and God will wipe away their tears, tears they will have because they will realise that they missed out on immortality and sharing Jesus' inheritance.
Galatians 4:5-7
(5) To redeem them that were under the law, that we might receive the adoption of sons.
(6) And because ye are sons, God hath sent forth the Spirit of his Son into your hearts, crying, Abba, Father.
(7) Wherefore thou art no more a servant, but a son; and if a son, then an heir of God through Christ.
The great multitude become servants, not sons.
Which suggest that it (verse 4) is referring to the resurrected Church and not to the great multitude that came through the great tribulation.
It's not in the Peshitta New Testament (which "is the only complete Aramaic New Testament known today which is held by a significant Christian denomination to be the original text written by the Apostles. The Church of The East has always held to this text as the original writing of the Apostles") which has (translated into English!):
4. And I saw seats, and they sat upon them, and judgment was given to them, and these souls who were cut off for the testimony of Yeshua and for the word of God, and because they did not worship The Beast, neither its Image, nor received a mark between their eyes or on their hands, they lived and reigned with The Messiah for one thousand years;
5. And this is the first resurrection.
6. Blessed and holy is he, whoever has part in the first resurrection, and the second death has no authority over these, but they shall be Priests of God and of The Messiah, and they shall reign with him one thousand years.
As above, I believe that the beast and mark appear (has already appeared) during the Gospel Age.
I believe that the second resurrection, of the rest of mankind (non-Christians), occurs at the beginning of the Millenium. After all, they are the ones being ruled over, being blessed and restored to perfection during the Millenium. The interpolation that "The rest of the dead didn’t live until the thousand years were finished" is a red herring! If it was to be interpreted in harmony with the rest of chapter 20, then you would have to understand that by "didn't live" it means that they don't gain eternal life until the end of the Millenium, after their judgement is finished, i.e.
(13) The sea gave up the dead who were in it. Death and Hades gave up the dead who were in them. They were judged, each one according to his works.
means that the rest of the dead are resurrected, and everyone living through the Millenium will be judged by their works during the Millenium, not by their works during their life before death (for Jesus' sacrifice has paid for their redemption, and forgiveness of sins, too).