Lot was sent by God to warn the people of Sodom and Gomorrah, hence the title (messenger)…unless you believe God just punished these cities without giving them a warning first…you may argue that he is a minor messenger,but still, he is a messenger.
Actually that wasn’t why he went to Sodom. See this relevant passage from the Bible:
So Abram went up from Egypt, he and his wife and all that he had, and Lot with him, into the Negeb.
Now Abram was very rich in livestock, in silver, and in gold. And he journeyed on from the Negeb as far as Bethel to the place where his tent had been at the beginning, between Bethel and Ai, to the place where he had made an altar at the first. And there Abram called upon the name of the LORD. And Lot, who went with Abram, also had flocks and herds and tents, so that the land could not support both of them dwelling together; for their possessions were so great that they could not dwell together, and there was strife between the herdsmen of Abram’s livestock and the herdsmen of Lot’s livestock. At that time the Canaanites and the Perizzites were dwelling in the land.
Then Abram said to Lot, “Let there be no strife between you and me, and between your herdsmen and my herdsmen, for we are kinsmen. Is not the whole land before you? Separate yourself from me. If you take the left hand, then I will go to the right, or if you take the right hand, then I will go to the left.” And Lot lifted up his eyes and saw that the Jordan Valley was well watered everywhere like the garden of the LORD, like the land of Egypt, in the direction of Zoar. (This was before the LORD destroyed Sodom and Gomorrah.) So Lot chose for himself all the Jordan Valley, and Lot journeyed east. Thus they separated from each other. Abram settled in the land of Canaan, while Lot settled among the cities of the valley and moved his tent as far as Sodom. Now the men of Sodom were wicked, great sinners against the LORD. [Genesis 13:1-13; ESV]
Lot didn’t go to Sodom to warn the people of their wickedness, he went there because his people and Abraham’s separated ways to avoid conflict.
As for God sending a warning beforehand…He actually intended to do that Himself. See this relevant passage:
Then the men set out from there, and they looked down toward Sodom. And Abraham went with them to set them on their way. The LORD said, “Shall I hide from Abraham what I am about to do, seeing that Abraham shall surely become a great and mighty nation, and all the nations of the earth shall be blessed in him? For I have chosen him, that he may command his children and his household after him to keep the way of the LORD by doing righteousness and justice, so that the LORD may bring to Abraham what he has promised him.” Then the LORD said, “Because the outcry against Sodom and Gomorrah is great and their sin is very grave, I will go down to see whether they have done altogether according to the outcry that has come to me. And if not, I will know.” [Genesis 18:16-21; ESV]
God dispatched two angels to reveal the true nature of the people of Sodom. We all know what happened when the angels arrived and ate with Lot.
But before they lay down, the men of the city, the men of Sodom, both young and old, all the people to the last man, surrounded the house. And they called to Lot, “Where are the men who came to you tonight? Bring them out to us, that we may know them.” Lot went out to the men at the entrance, shut the door after him, and said, “I beg you, my brothers, do not act so wickedly. Behold, I have two daughters who have not known any man. Let me bring them out to you, and do to them as you please. Only do nothing to these men, for they have come under the shelter of my roof.” But they said, “Stand back!” And they said, “This fellow came to sojourn, and he has become the judge! Now we will deal worse with you than with them.” Then they pressed hard against the man Lot, and drew near to break the door down. [Genesis 19:4-9; ESV]
The people of Sodom essentially had a chance to prove themselves before the Lord, but their evil actions made their wickedness evident. I often laugh at this, because in the previous chapter God confirms to Abraham that for the sake of ten righteous men He will spare the city (Gen 18:32), and the first thing the people of Sodom do is try to rape the angels.
All in all, there is no evidence that Lot was sent to Sodom and Gomorrah to warn the people of their wickedness, nor that he was either a prophet nor messenger - let alone a “minor” messenger.