God commands us to do it. That is all you need to know.
You need to read Romans 9...when Paul talked about this very topic he had the same objections (there is nothing new under the sun).
You know what he said? The gist is this: Who are you to question God, oh man?
Well, just who are you to question God's ways, Petronski?
I question your nutty certainty that you've got it all figured out. You've reduced God to a trigonometry proof. It's amazing.