"For when God made promise to Abraham, because he could swear by no greater, he sware by himself," Hebrews 6:13. It seems that God can swear by himself. I tend to think of this Rev 10 messenger as a picture of Christ.
This verse here that you quoted is the crowning jewel that proves that the preincarnate Jesus Christ is not an actual angel but God Almighty. The writer of Hebrews is referring back to Genesis 22. Look at Genesis 22:11, "But the angel of the Lord called to him from heaven, and said, "Abraham, Abraham!" And he said, Here I am." Vs12, "And he said, Do not stretch out your hand against the lad, and do nothing to him, for know I know that you fear God, since you have not withheld , your only son from me." (As a side not Abraham had other sons but Isaac was the son of promise).
Vs15, "Then the angel of the Lord called to Abraham a second time from heaven, vs16, and said, By Myself I have sworn, declares the Lord, because you have done this thing, and have not withheld you son, your only son, vs17, indeed I will greatly bless you and I will greatly multiply your seed as the stars of the heavens, and as the sand which is on the seashore; and your seed shall possess the gate of their enemies."
So, when someone insists that the angel of the Lord is an actual angel simply refer them to Hebrews 6:13-17. Now, there is another argument the Jews use to discount the role of Jesus in Genesis 22. They say Jesus or this angel if you will is simply a "shaliah." In other words, one person is the "agent" and he agrees to do something for another party, known as the "principal," in this case (that is at Genesis 22) God is the principal and Jesus represents Him.
The problem with this scenario we have before us is the fact that the agent (according to the Jewish Library) has limitations to his duties. Again, in this case the agent can not swear an oath on behalf of the principal. That's what we have here as clear as day as stated at Hebrews 6:13-17. Nehemiah6 is correct by quoting Revelation 10:6. Notice here even the angel swears the oath on the basis of the living God.
If you happen to witness a murder and you are called on to testify what you say, you cannot send your Uncle Harry to testify for you. Furthermore, let's say you cannot appear in court for some reason, the court will send someone to you and they will "depose" you as a witness. Hope this helps.
IN GOD THE SON,
bluto