Question: "What is the first resurrection? What is the second resurrection?"
Answer: Daniel 12:2 summarizes the two very different fates facing mankind: "Many of them that sleep in the dust of the earth shall awake, some to everlasting life, and some to shame and everlasting contempt." Everyone will be raised from the dead, but not everyone will share the same destiny. The New Testament reveals the further detail of separate resurrections for the just and the unjust.
Revelation 20:4-6 mentions a "first resurrection" and identifies those involved as "blessed and holy." The second death (the lake of fire, Revelation 20:14) has no power over these individuals. The first resurrection, then, is the raising of all believers. It corresponds with Jesus' teaching of the "resurrection of the just" (Luke 14:14) and the "resurrection of life" (John 5:29).
The first resurrection takes place in various stages. Jesus Christ Himself (the “first fruits,” 1 Corinthians 15:20), paved the way for the resurrection of all who believe in Him. There will be the resurrection of “the dead in Christ” at the Lord’s return (1 Thessalonians 4:16) and the resurrection of the martyrs at the end of the tribulation (Revelation 20:4). The Old Testament saints will also be raised at the end of the tribulation, and they are also part of the first resurrection.
Revelation 20:12-13 identifies those comprising the second resurrection as the wicked judged by God at the great white throne judgment prior to being cast into the lake of fire. The second resurrection, then, is the raising of all unbelievers; the second resurrection is connected to the second death. It corresponds with Jesus' teaching of the "resurrection of damnation" (John 5:29).
The event which divides the first and second resurrections seems to be the millennial kingdom. The last of the righteous are raised to reign "with Christ a thousand years" (Revelation 20:4), but the "rest of the dead [that is, the wicked] lived not again until the thousand years were finished" (Revelation 20:5).
What great rejoicing will attend the first resurrection! What great anguish at the second! What a responsibility we have to share the Gospel! "And others save with fear, pulling them out of the fire" (Jude 23).