John saw that this mighty angel “raised his right hand to heaven” to swear an oath. (Note: in one of his hands this angel still held the open scroll, perhaps now raised to heaven, perhaps not.) In Scripture the right hand is often a symbol of power (see Exodus 15:6; Psalm 18:35; Psalm 20:6; Psalm 118:15–16; Isaiah 48:13, etc.) By raising this hand to heaven this mighty angel is declaring his ability to make happen what he swears he will do.
5 And the angel whom I saw standing on the sea and on the land raised his right hand to heaven