Christian redemption system

I've been asking this question to many peoole and on many forums etc over the past maybe 5 yrs and i've not yet recieved an answer that makes sense.

Without getting to deep into the setup of the question ill just get straight to it.

If god (assuming one exists) decided that the punishment for sin is death (physical, spiritual or whatever you want) why would he then go and kill part of himself (Jesus) to prevent himself from having to carry out the punishment which he himself decided?

Seems kind of futile to me.