The sounding of the angels will be in response to the prayers of the saints which were offered with incense before the throne. Since the judgments are now to be of a greater severity than the previous six seals, great solemnity attends the moment.
The Old and New Testaments use the trumpet as the symbol of Gods intervention in history (e.g., Ex. Ex. 19:16, Ex. 19:19; Isa. Isa. 27:13; Joel Joel 2:1; Zep. Zep. 1:16; Zec. Zec. 9:14; Mtt. Mat. 24:31; 1Cor. 1Cor. 15:52-53; 1Th. 1Th. 4:16). A trumpet blast can mean one of three things in Scripture: first, an alarm; second, a fanfare to announce royalty; third, a summons to battlethe latter is appropriate in this context.1
No doubt, these angels had been waiting for this particular ministry for a long time. As ministering spirits, sent forth to minister for them who shall be heirs of salvation (Hebrews Heb. 1:14), all of Christs mighty angels (2 Thessalonians 2Th. 1:7) are intensely occupied with the progress of His work of salvation on earth, which things the angels desire to look into (1 Peter 1Pe. 1:12). The seven presence angels were surely the most concerned of all, and they were fully prepared.2
1 Monty S. Mills, Revelations: An Exegetical Study of the Revelation to John (Dallas, TX: 3E Ministries, 1987), Rev. 8:6.