Compared with the rest of the story, there is a sudden change in the pronouns from plural to singular. Notice verse 17, "So it came to pass, when they had brought them outside, that he said"—one of the messengers speaks. In verse 18, Lot addresses them and uses the term "lords." Keil & Delitzsch Commentary says, No, "lord" is singular in the Hebrew.
Adonai, "Lord," is the name of God. Is it the name of Melchizedek? Was Melchizedek there to destroy the city? If the messenger was not Melchizedek, why did Lot call him "lord"? Why in verses 21 and 22 does the angel take the authority to himself to destroy the city? He says to Lot, "I cannot do anything until you arrive there," and then verse 24 relates, "The LORD rained down. . . ." Is the LORD the same "lord" who was the "I" of verse 22? An interesting sequence of verses.
Not only does Keil & Delitzsch say this, but the Jewish Publication Society's Tanahk, the King James Version, and the Revised Standard Version all reinforce this idea in various ways.
John W. Ritenbaugh
Faith (Part Four)
These angels had power; they say directly they were the ones who would destroy the city. That power and the authority to do that had been delegated to them by God. They had authority to get Lot and his family out of the city, and they had delegated authority to punish the cities.
Consider that God did not script everything out for them. What does that mean to us? Like men, these angels had minds, and they had to think things through. Is this in line with the charges that God gives us? In the situations we find ourselves in, we have to think, "Would this be okay? What are our alternatives here?" In other words, the angels did not just march into the city, commandeer what they needed, grab Lot by the seat of his pants, and throw him unceremoniously outside of the city. They had the authority to allow Lot choices, and they worked within the framework God had given them. This means that angels have minds with which to assemble facts, to think, and to devise alternatives.
John W. Ritenbaugh
Image and Likeness of God (Part Three)