This question puzzled me for decades, but I finally formulated an answer, for my kids as they grew up.
God, being God, is “extremely” everything that He is.
God is an extreme altruistic lover.
God is extremely sovereign.
God is extremely just.
God the extreme altruistic lover, being overflowing with love, desired to create love objects with Whom He could enter into a love relationship, in which each would love the other and be loved by the other.
But, this posed a problem. God, the extreme sovereign, is innately unable to create equals in any substantial sense. The concept of God creating an equal is a “square circle.” That God can’t do this is something which is “in and of God.”
So, when God created us to have a love relationship with us, He necessarily made “contingent” beings – beings utterly reliant on Him for continued existence, who are only made “in His image and likeness.” We are not gods.
Contingent beings with an intellect and free will have a problem: Without more – specifically, without grace – they are like Eve before the fall; they are innately insecure, and aware of their insecurity, and so philosophically poised to make the sinful choice, when they exercise their free wills, every single time.
Without grace, our kind are “sin machines,” poised to rebel, rebel, rebel, sin, sin, sin, so that without grace we would exist in an ongoing state of alienation from God.
Original Sin was not an incident in time, committed in contradiction to grace. That is what our sins now, are. But not Original Sin.
Original Sin is the filiation with evil endemic to our flesh in the absence of grace.
Now, God did not err when He made us. He did not “forget” grace. He knew that we would be like this.
So, God planned, from before our creation, to make grace accessible to us, as our “final ingredient.”
But here God’s extreme justice “kicks in.” In response to God’s plan to provide grace, God’s Own extreme justice responds, “Whoa! Hold on one second! Grace is a ticket to Heaven – to shaking hands with God, so to speak! There are NO freebies! There are NO pennies from Heaven! No! SOMEONE has got to PAY for this grace!”
The Second Person of the Divine Trinity, overflowing with love, said, “I WILL! I VOLUNTEER TO PAY THE PRICE FOR GRACE EXACTED BY OUR OWN JUSTICE! Since the sin ungraced humans are inclined to leads to suffering and death, the price exacted by Our Own justice is suffering and death. I volunteer to suffer and die to buy the grace needed as a final ingredient for humans.”
God the Father responded, “I lovingly accept your love offering, and so I offer you up to suffer and die horribly.”
And the rest is history. Christ was tortured and murdered horribly. This paid the price of grace exacted by God’s Own extreme justice. Grace flowed forwards and backwards through time.
That is why Jesus HAD TO suffer and die.