God sacrificed himself to himself to forgive us. Another nonsense from the bible right there. It makes absolutely no sense and we are not even saved, we are still here, aren't we? Why did an omniscient and all powerful god need to sacrifice his ''son'' to forgive humanity? Why not just forgive us? What is there to forgive anyways, he already knew everything that would happen.
This is a complex question Astargath. To start with we must understand what the Bible means when it talks of sacrifice. That in itself is a very deep topic. I believe Jordan Peterson articulates it far better then I could so I have linked to his discussion of Biblical sacrifice below.
Biblical Series V: Cain and Abel: The Hostile Brothers
Once we understand the purpose and meaning of sacrifice we can move on to the second part of your question why might tremendous sacrifice from heaven be necessary to save humanity?
To try to grasp this it is helpful to try and imagine what the world would be like without Christianity.
This is very difficult to do because Christianity is the foundation western culture was built upon so you have to return back to 100 AD or so and envision an alternative future world starting with a collapsing Roman Empire.
The power of Christianity in reshaping the world cannot be understated. We see this in the transformation of Russia as it returns to its orthodox roots. We see it in the rapid transformation of China where Christianity is currently spreading like wildfire laying the foundation of a post communistic future. It is perhaps most clearly displayed on the Korean Peninsula where a people with a shared culture, race, and average IQ is split into two halves with Christianity punished with death in one and widely embraced in the other.
The argument that Christianity and the sacrifice at its heart was necessary to save mankind is not a trivial one. Given the facts on the ground it could very well be true in more ways then we know.