The purpose of this angel is clear to announce the final judgments on the earth. His right foot on the sea and left foot on the earth. His right foot on the sea and left foot on the earth indicate that his words deal with all creation, not just a limited part as with the seal and trumpet judgments. The seventh trumpet will usher in the seven vial judgments which will bring an end to the present world. When this universal judgment comes, God's truth will prevail.
There was another powerful angel coming down out of heaven wrapped in a cloud. There was a rainbow over his head, his face was sun-radiant, his les pillars of fire. He had a small book open in his hand. He placed his right foot on the sea and his left foot on land, then called out thunderously, a lion roar. When called out, the seven thunders called back. When the seven thunders spoke, I started to write it all down, but a voice out of Heaven stopped John saying, "Seal with silence the seven thunders; don't write a word."
The first contains a revelation of judgments against evil. The contents of the second title scroll are not indicated, but it also may contain a revelation of judgment.
Throughout history people have wanted to know what would happen in the future, and God reveals some of it in this book. But John was stopped from revealing certain parts of his vision. An angel also told the Prophet Daniel that some vision he saw were not to be revealed yet to everyone, and Jesus told his disciples that the time of the end is known by no one but God. God has revealed all we need to know to live for him now. In our desire to be ready for the end, we must not place more emphasis on speculation about the last days that on living for God.
Then the angel John saw astride sea and land lifted his hand to Heaven and swore by the One Living Forever and Ever, who created Heaven and everything in it, earth and everything in it, sea and everything in it, that time up-that when the seventh angel blew his trumpet, with he was about to do, the Mystery of God, all the plans he had revealed to his servants, the Prophets, would be completed.
Reference summary used from The Message Bible and The Life Application Bible, KJV, Tyndale Publishers, Inc., Wheaton, IL