A.T. Robertson Commentary Revelation 8:6

"And the seven angels that had the seven trumpets prepared themselves to sound." — Revelation 8:6 (ASV)

Prepared themselves (ητοιμασαν αυτους). First aorist active indicative of ετοιμαζω. They knew the signal and got ready.

To sound (ινα σαλπισωσιν). Sub-final (object) clause with ινα and the first aorist ingressive active subjunctive of σαλπιζω. The infinitive could have been used.