Greetings! Chiming in here.
I think its important to understand that the Bible is book of faith, not a book of history.
We have to have faith because, as humans, we cannot fully comprehend God and his will. I look at it as when you try to communicate with you pet. The pet doesn't always fully understand what you mean, but it is able to understand some of it.
The Old Testament has many scriptures which point to the coming of Christ.
As Christians, we are able to celebrate His death because there is now a way to be closer to God despite our sinfullness and non-comprehension.