The fire he came to cast upon the "earth" [IE: the promised land] is the divine fire of judgment upon Israel (66-73ad):
Isa 9:19 KJV - 19 Through the wrath of the LORD of hosts is the land darkened, and the people [IE: "the people" = "the Jews"] shall be as the fuel of the fire: no man shall spare his brother.
Jer 15:14 KJV - 14 And I will make thee to pass with thine enemies into a land which thou knowest not: for a fire is kindled in mine anger, which shall burn upon you.
Jer 17:4 KJV - 4 And thou, even thyself, shalt discontinue from thine heritage that I gave thee [IE: the promised land]; and I will cause thee to serve thine enemies in the land which thou knowest not: for ye have kindled a fire in mine anger, which shall burn for ever.
Jer 43:12-13 KJV - 12 And I will kindle a fire in the houses of the gods of Egypt [IE: Israel]; and he shall burn them, and carry them away captives: and he shall array himself with the land of Egypt, as a shepherd putteth on his garment; and he shall go forth from thence in peace. 13 He shall break also the images of Bethshemesh, that is in the land of Egypt; and the houses of the gods of the Egyptians shall he burn with fire.
Eze 21:32 KJV - 32 Thou shalt be for fuel to the fire; thy blood shall be in the midst of the land; thou shalt be no more remembered: for I the LORD have spoken it.
Joe 2:3 KJV - 3 A fire devoureth before them [IE: the invading army]; and behind them a flame burneth: the land is as the garden of Eden before them, and behind them a desolate wilderness; yea, and nothing shall escape them.
Nah 3:13 KJV - 13 Behold, thy people in the midst of thee are women: the gates of thy land shall be set wide open unto thine enemies: the fire shall devour thy bars.
Zep 1:18 KJV - 18 Neither their silver nor their gold shall be able to deliver them in the day of the LORD'S wrath; but the whole land shall be devoured by the fire of his jealousy: for he shall make even a speedy riddance of all them that dwell in the land.
So is what he says next related? I believe so. He is rueing the period between this moment in which he is having this interchange and when the fire falls. Why? Because it is hard to kick against the pricks:
Num 33:55 KJV - 55 But if ye will not drive out the inhabitants of the land from before you; then it shall come to pass, that those which ye let remain of them shall be pricks in your eyes, and thorns in your sides, and shall vex you in the land wherein ye dwell.
Jesus clarifies that the problem is not the Romans but rather the Jews that are the enemies of God's elect ("the Israel of God"). Jesus came to put a sharp line between God's people and the apostate Jews with the result that the latter will persecute the former:
Mat 10:23 KJV - 23 But when they persecute you in this city, flee ye into another: for verily I say unto you, Ye shall not have gone over the cities of Israel, till the Son of man be come.
Mat 23:34 KJV - 34 Wherefore, behold, I send unto you prophets, and wise men, and scribes: and some of them ye shall kill and crucify; and some of them shall ye scourge in your synagogues, and persecute them from city to city:
Luk 11:49 KJV - 49 Therefore also said the wisdom of God, I will send them prophets and apostles, and some of them they shall slay and persecute:
Luk 21:12 KJV - 12 But before all these, they shall lay their hands on you, and persecute you, delivering you up to the synagogues, and into prisons, being brought before kings and rulers for my name's sake.
Jhn 5:16 KJV - 16 And therefore did the Jews persecute Jesus, and sought to slay him, because he had done these things on the sabbath day.
Jhn 15:20 KJV - 20 Remember the word that I said unto you, The servant is not greater than his lord. If they have persecuted me, they will also persecute you; if they have kept my saying, they will keep yours also.
At the heart of the matter is the "offense of the cross":
Gal 5:11 CSB - 11 Now brothers and sisters, if I still preach circumcision, why am I still persecuted? In that case the offense of the cross has been abolished.
I would distill the above verse down to saying that when the agenda of God clashes with those in power under a different system there will be persecution:
Jhn 7:7 NET - 7 The world cannot hate you, but it hates me, because I am testifying about it that its deeds are evil.
1Jo 3:12 NET - 12 not like Cain who was of the evil one and brutally murdered his brother. And why did he murder him? Because his deeds were evil, but his brother's were righteous.
The offense is that Jesus is invalidating the hiding place of the corrupt rulers of Israel:
Isa 56:7 KJV - 7 Even them will I bring to my holy mountain, and make them joyful in my house of prayer: their burnt offerings and their sacrifices shall be accepted upon mine altar; for mine house shall be called an house of prayer for all people.
Mar 11:17 KJV - 17 And he taught, saying unto them, Is it not written, My house shall be called of all nations the house of prayer? but ye have made it a den [IE: a "refuge"] of thieves. Even when these thieves witnessing other thieves being transformed they still did not repent and believe:
Mat 21:31-46 CSB - 31 "Which of the two did his father's will? " They said, "The first." Jesus said to them, "Truly I tell you, tax collectors and prostitutes are entering the kingdom of God before you. 32 "For John came to you in the way of righteousness, and you didn't believe him. Tax collectors and prostitutes did believe him; but you, when you saw it, didn't even change your minds then and believe him. 33 "Listen to another parable: There was a landowner, who planted a vineyard, put a fence around it, dug a winepress in it, and built a watchtower. He leased it to tenant farmers and went away. 34 "When the time came to harvest fruit, he sent his servants to the farmers to collect his fruit. 35 "The farmers took his servants, beat one, killed another, and stoned a third. 36 "Again, he sent other servants, more than the first group, and they did the same to them. 37 "Finally, he sent his son to them. 'They will respect my son,' he said. 38 "But when the tenant farmers saw the son, they said to each other, 'This is the heir. Come, let's kill him and take his inheritance.' 39 "So they seized him, threw him out of the vineyard, and killed him. 40 "Therefore, when the owner of the vineyard comes, what will he do to those farmers? " 41 "He will completely destroy those terrible men," they told him, "and lease his vineyard to other farmers who will give him his fruit at the harvest." 42 Jesus said to them, "Have you never read in the Scriptures: The stone that the builders rejected has become the cornerstone. This is what the Lord has done and it is wonderful in our eyes? 43 "Therefore I tell you, the kingdom of God will be taken away from you and given to a people producing its fruit. 44 "Whoever falls on this stone will be broken to pieces; but on whomever it falls, it will shatter him." 45 When the chief priests and the Pharisees heard his parables, they knew he was speaking about them. 46 Although they were looking for a way to arrest him, they feared the crowds, because the people regarded him as a prophet.
So the mention of the coming judgment and the uncomfortable delay refer to the baptism of fire that Jesus himself would personally experience ("I have a Mikveh in which to be immersed") in the form of deadly persecution by the Jewish leaders. The nation would be split in two:
Gal 4:28-31 CSB - 28 Now you too, brothers and sisters, like Isaac, are children of promise. 29 But just as then the child born as a result of the flesh persecuted the one born as a result of the Spirit, so also now. 30 But what does the Scripture say? "Drive out the slave and her son, for the son of the slave will never be a coheir with the son of the free woman." 31 Therefore, brothers and sisters, we are not children of a slave but of the free woman.