The answer to your question is that the first resurrection (which pertains strictly to Christ and His saints) occurs in THREE PHASES. Just like a Hebrew harvest.
1. THE FIRST FRUITS -- the resurrection of Christ and some of the saints at that time
2. THE MAIN HARVEST -- the Resurrection/Rapture of the Church
3. THE GLEANINGS -- the Tribulation saints which were beheaded by the Antichrist
1 CORINTHIANS 15
20 But now is Christ risen from the dead, and become the firstfruits of them that slept...
23 But every man in his own order: [1] Christ the firstfruits; [2] afterward they that are Christ's at his coming.
24 [3] Then cometh the end, when he shall have delivered up the kingdom to God, even the Father; when he shall have put down all rule and all authority and power.