There are two reasons Christ died on the cross: First -- and most important -- He was the sacrificial lamb offered by God to balance out the sins of the world. God allowed His son to be subjected to the same injustice that human beings are subjected to by their fellow humans; God did not protect Him or shield Him.
Only by suffering the same injustice we impose on one another is God through Christ able to forgive all sins and transgressions. Only He has uniquely been without sin, without blame; that gives only Him the unique position of being able to forgive what was done to Him without having to ask forgiveness in return.
"Forgive us our sins as we forgive those who sin against us" is both a formula and a warning: If we want grace & forgiveness, we have to offer it.
That’s the spiritual / metaphysical / theological reason He had to die.
But there’s a far more mundane reason that motivated the political charges against Him.
Though He was accused of treason, sedition, and rebellion, Pontius Pilate clearly didn’t believe Jesus was guilty of anything except being a pain in the tuches; he kept looking for reasons to release Him. Even Herod couldn’t whip himself up into a frenzy over His purported treason (since Herod was King of Judea, and Jesus was one of his citizens, a treason charge from him would be valid).
The motive behind the Pharisees’ false accusations was purely monetary:
The Roman governor had to approve each new High Priest appointment. While the Pharisees would make the nomination, by treaty the governor had final authority.
The same family -- Annas and his sons & son-in-law Caiaphas -- had a lock on that chair for most of Christ’s ministry. They were probably afraid that the Romans -- who couldn't have cared less about justice or morality or theology but just wanted law-n-order so the tax revenues would keep flowing -- would learn that very, very few Judeans gave a fig for the Pharisees in general & the High Priest (whoever the current office holder was) in particular.
They were also doubtlessly afraid that the Romans had heard thru spies that this radical new preacher who was winning followers in ever increasing numbers had taught several points in regards to Rome & Roman authority...
“So tell me, centurion, what have you learned of this man Jesus. Has he made any statements regarding Rome or Caesar?”
“Aye, Pilate, he has.”
“You can’t trust these firebrands. Very well, what has he said?”
“Well, first he has told the Jews that they should pay the taxes that Caesar has imposed.”
“I’m sorry, I could have sworn you just said he told them to pay their taxes.”
“Aye, he did. ‘Render unto Caesar’ are his exact words according to our spies.”
“I see. Anything else?”
“He told his followers that if a Roman tells them to carry his armor one mile, they are to carry it two.”
“Has he said anything rebellious? Anything urging the people to fight back?”
“No, lord Pilate; quite the opposite in fact. He said if someone strikes them on one cheek they are to turn and offer the other cheek as well.”
“He said that?”
“Aye.”
“And he still has followers?”
“Aye, and in greater and greater numbers.”
“I’m curious: Has this man Jesus ever actually met a Roman?”
“Aye, Pilate, he has. He met me.”
“You?”
“Aye. My most loyal servant was sick and Jesus was performing healings in the town square. I went to him and asked him to heal my servant.”
“And did he come and heal him?”
“Well, yes and no…he indicated he was willing to come but I said that would not be necessary, seeing as how he was a man of great authority. And as a fellow man of authority I know if I give an order it will be obeyed, so I told him all he had to do was say the word and I knew my servant would be healed.”
“And he did so?”
“Aye, at that very moment even though he was far away.”
“Did he make any comment on this?”
“Aye, he said he hadn’t met any Jews who had as much faith in him as I had.”
“He said that.”
“Aye.”
“So, let me see if I understand you: You’re telling me that Jesus tells his followers to pay taxes to Caesar, to carry a Roman’s armor an extra mile if ordered to carry it one, and to turn the other cheek and submit to authority, and on top of all this not only healed your servant but said you had more faith than the Jews?”
“Aye.”
“Hmmm, centurion, y’know who might make a good High Priest…?”