Apocalypse Revealed #415
415. And I looked, and I heard an angel flying in the midst of heaven. (8:13) This symbolizes instruction and prediction from the Lord.
In the highest sense an angel means the Lord, and so also something from the Lord (no. 344). And to fly in the midst of heaven and speak means, symbolically, to perceive and understand, and when said of the Lord, to foresee and provide (no. 245). But here it means to instruct and predict.
Earth, kingdoms, and world
In Isaiah 14:16, 17, these signify respectively the church, its truths, and its goods. (Apocalypse Explained 730[5])