What does Revelation 10:5 mean?

In this verse John reports that he saw the mighty angel, whose feet rested on the sea and the land, raise his right hand to heaven. Holding the open scroll in one hand, the mighty angel raised his right hand to heaven in preparation for an oath.

This gesture commonly preceded a solemn oath in Scripture. When Abraham refused a reward from the king of Sodom, he said, "I have lifted my hand to the LORD, God Most High, Possessor of heaven and earth, that I will not take a thread or a sandal strap or anything that is yours, lest you should say, 'I have made Abram rich'" (Genesis 14:22–23). In the Song of Moses, Moses declared, "I lift up my hand to heaven and swear" (Deuteronomy 32:40).

In Daniel 12:7 we read Daniel's declaration: "I heard the man clothed in linen, who was above the waters of the stream; he raised his right hand and his left hand toward heaven and swore by him who lives forever that it would be for a time, times, and half a time, and that when the shattering of the power of the holy people comes to an end all these things would be finished."