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.