‘And I saw another sign in heaven, great and marvellous, seven angels having seven plagues which are the last, for in them is finished the wrath of God.'
The seven plagues are the last to be described not the last chronologically, for the seven seals and the seven trumpets which run parallel to them also involved the wrath of God. They are the last because they sum up God's judgments. As Paul emphasised ‘the wrath of God IS (at this present time) revealed from Heaven' (Romans 1:18 compare Ephesians 5:6; Colossians 3:6; Romans 5:9) for we are ‘by nature children of wrath' (Ephesians 2:3).
The idea of the wrath of God is applied to the final judgment, ‘the day of wrath' (Romans 2:5; Romans 2:8; Matthew 3:7; Luke 3:7; John 3:36; Rom 9:22; 1 Thessalonians 1:10; 1 Thessalonians 5:9; Revelation 6:16-17; Revelation 11:18; Revelation 14:10; Revelation 14:19; Revelation 19:15) and to the present wrath of God revealed in various ways (Luke 21:23; Romans 1:18 with Romans 1:24-32; 1 Thessalonians 2:16; Revelation 15:1; Revelation 15:7; Revelation 16:1; Revelation 16:19). It is not anger as we know it but righteous anger like the anger of Jesus (Mark 3:5), a righteous response to the awfulness of sin, the sign of an antipathy to sin. In His holiness God must react against sin.
He did it first by offering a way of redemption and providing a means of ‘propitiation' through Jesus Christ and His death on the cross (Romans 3:25; 1 John 2:2), which was a way of righteously dealing with sin while forgiving the sinner, but for those who refuse that way His wrath against sin means that He must ultimately deal with sinners, first by attempts to make them consider their ways, and then in final judgment.
‘Another sign in heaven, great and marvellous', compare the signs in Revelation 12:1; Revelation 12:3. We have seen the sign speaking of the true people of God, we have seen the sign of the Evil One who seeks to destroy God's handywork, now we see the sign of God's response to that evil, seven angels having the seven plagues which finalise God's programme of wrath against sin. But before these are emptied we must see the safety of the redeemed.
The fact that there is no article before ‘angels' suggests these are not the seven angels, but merely seven selected from among many. It is not, however, a matter of great importance. What matters is that Heaven is at work.