First of all, the notion that Jesus was “punished” on our behalf is a total fallacy - more on that later. But first:
To understand why God had to send Jesus, and why Jesus had to go through the brutal suffering and crucifixion to save us, we first have to understand the nature of reality.
Love = Life.
Hate = Death.
God is Love, therefore God is the source of life.
If we don’t love, we disconnect from life itself.
Disconnect from life - we whither and die.
This is the nature of reality.
If we understand that as soon as we sin, we sever ourselves from the life source, then we understand that we cannot live forever. We are mortal. We are slowly dying. We are dead. The only way we can live forever, is to live a perfectly righteous life, full of love. But this is impossible. As hard as we try, we cannot do this. So God, in his infinite love for us, not wishing to see any one of his beloved die, comes into the world as a human being, to live that perfect life ON OUR BEHALF. He lives a totally righteous life of perfect pure love as a human being. What happens as a result? Literally everything he encounters is restored and ordered. The blind, the sick, the dead, the storms. Death cannot hold perfect love and righteousness. So he rises from the dead. And the key is this: He raises us all up with him. How does this work? Because by coming into the world, he becomes person, meaning he enters a personal relationship with each one of us, marries himself to us, becomes ONE with us. What happens to him, happens to us. That is how love works. It unites.
So what about all this talk about appeasing God? Substitutionary atonement? Jesus paying a ransom? Expiation?
Well, the idea that Jesus had to come to be “punished” in our place because somehow sin demands punishment by an angry God, and that instead of punishing us, God punishes his son, is absolute hogwash. In fact, the Church fathers even went as far as to say it was heresy. The whole substitutionary atonement idea, where Jesus is punished in our place, is a gross misunderstanding born out of Western Christianity. It is not true. God did not send his son Jesus to be punished and die on the cross instead of us, to somehow appease the Father. This is a totally false. God was not looking for someone to punish because of our sin. Rubbish.
The Orthodox understanding is that the language used to describe Jesus’ death - ransom, atonement, redemption, scapegoat, expiation - is all symbolic language. The “ransom” Jesus pays is to the “natural order”. The way things are naturally, a natural law so to speak, mean that perfect righteousness means life - so Jesus “pays” a perfect life, as a human being, to the cosmos, which results in eternal life. Atonement means making things right - and that’s exactly what Christ does. Not in the sense of appeasing God, but in the sense of fulfilling what we each need to do to live eternally, but cannot - he does it on our behalf and grafts himself to us, so that we may experience it also, being one with him.
If you really think about it, this is the only way it could be. It has to be this way. It is inevitable from the moment of creation.