For the record, I would like to assure the saints that I believe that Christ's second coming is future from now.
However, Christ Jesus our Lord commanded John the Revelator to write what he saw (and heard, etc.) and send it to seven Asian Churches of the first century.
So, if the text of what John wrote to the 7 Asian Churches did not have meaning for their first-century time frame, then there is no real point to the book of Revelation in general.
There is indeed a reason for the "first resurrection"--and that reason has to do with the reality that the saints in this verse (in bold below):
8“I am the Alpha and the Omega,” says the Lord God, “who is and who was and who is to come, the Almighty.”
9I, John, your brother and fellow partaker in the tribulation and kingdom and perseverance which are in Jesus, was on the island called Patmos because of the word of God
I'm sure that we all remember the reasons for Judah's captivity in Babylon to begin with:
II Chron. 36
15 The LORD, the God of their fathers, sent word to them again and again by His messengers, because He had compassion on His people and on His dwelling place;
16 but they continually mocked the messengers of God, despised His words and scoffed at His prophets, until the wrath of the LORD arose against His people, until there was no remedy.
From time to time, the notion that "The Beast" of the book of Revelation is only a future entity from now is given a great consideration by the saints.
However, the witness/martyr Saint Stephen was killed in the 1st century.
And Revelation 18:24 states the following:
24 “And in her (Mystery Babylon) was found the blood of prophets and of saints and of all who have been slain on the earth.”
Let's look at these verses again from Rev. 20 apropos the first resurrection:
4 Then I saw thrones, and they sat on them, and judgment was given to them. And I saw the souls of those who had been beheaded because of their testimony of Jesus and because of the word of God, and those who had not worshiped the beast or his image, and had not received the mark on their forehead and on their hand;