Most people believe these 2 things about a 'God'.
He is all powerful
He is all knowing
There is the age old pholisophical debate about how you reconcile this with the problem of evil. Perhaps he's all powerful but misses bits, or all knowing but can't do a damn thing about it. Neither of these represents a Christian God though.
So, it's argued that free will helps to build our souls.
Or we need to experience evil to understand and enjoy good.
Or we need be able to choose the path of goodness, which means the possibility of evil exists.