- You can believe in God; If it exists, then you will go to heaven.
We can believe in God, and have serious doubts about the existence of any such place.
God is just a name for the prima causa of things within our experience, we can not conceive existence without a prima causa. It is an axiome - we must take it for true to develop theories and religions.
Still, it does not answer the question of the prima causa of the existence of God itself.