'But each in his own order, Christ the firstfruits, then those who are Christ's, at his coming. Then the end, when he has delivered up the Kingly Rule to God, even the Father, when he has abolished all rule and all authority and power.'
But the predetermined order must be fulfilled. First will be Christ, the firstfruits, then those who are Christ's at His coming. The firstfruits will be followed by the harvest. For at His coming the dead in Christ will rise first, and then those who are alive will be caught up, transformed and will meet the Lord in the air, and so we shall ever be with Him (1 Corinthians 15:52; 1 Thessalonians 4:13-18). The harvest will have been gathered in.
'Then the end.' Once the resurrection has taken place, and the harvest has been gathered, it will be the end. Then Christ the King will deliver up the Kingly Rule to God, even the Father, and then will He abolish all rule and authority and power. As vividly depicted in Revelation 19:11-21 the Enemy will be defeated, the rebels judged, and Christ will be finally triumphant over all evil in process of yielding all to the Father.
Note the close connection between the abolishing of all rule and all authority and power and the delivering up of the Kingly Rule to God. The one follows close on the other, indeed are almost instantaneous. Both verbs are active aorist subjunctives.
The natural significance of these words is that 'then the end' follows immediately on the resurrection. Once the final resurrection has taken place, death has been destroyed, and nothing remains but the final triumph, when that which began with God is fully restored to God, so that He can be all in all (1 Corinthians 15:28). (But those who believe in a Millennium to come, which does not appear to fit in here, have to leave a gap so as to allow for it. But there is no room for a gap. The resurrection of His people results in the end of all earthly things. That finalises redemption. There is no point in anything further. And can we seriously think that someone who believed in the Millennium would have given no hint of it here?).
'He shall have abolished all rule and all authority and power.' Paul regularly refers to the heavenly antagonists of God in these and similar terms. Satan rules the 'power (= the kingdom with all its powers of evil) of darkness' (Colossians 1:13), he is the 'prince of the power (all that contributes to the power of his kingdom) of the air' (Ephesians 2:2). See also Romans 8:38; Ephesians 1:21; Ephesians 3:10; Ephesians 6:12; Colossians 1:16; Colossians 2:10; Colossians 2:15). Their rule and power will be rendered void, their positions of authority will be abolished, defeated through the cross.