Andrew of Caesarea
Saint John often uses the number of seven angels, because it corresponds to this age, to sabbath rest, and to the repose of the saints. Therefore the opening of this seventh seal indicates the passage from earthly life.
The seven angels assist this passage by striking those men who need correction and instruction. The silence signifies good order, reverence, and the angels' ignorance of the time of the Second Coming.
The half hour is a short time when, after the punishments and the end of the world, the Kingdom of Christ will come.