Some religions, such as Christianity, posit the existence of a perfect God who is all-loving, all-knowing, and all-powerful.
This leads to the awkward question of how a perfect God could allow innocent people to suffer.
It’s one thing to say that people have Free Will, and they must face the consequences of their own actions. That, at least, seems fair. But plenty of people suffer in some way due to no fault of their own. Sometimes infant children get diseases and die. Why does God allow that? He’s all-loving, so of course he wants to help the children. He’s all-knowing, so of course he’s aware of their plight. And he’s all-powerful, so it should be easy for him to cure the disease instantaneously. And yet, infant children still die sometimes. Why is that?
It would be so much easier on the theists if they just posited a belief in a limited God. Suppose there is a God who is definitely all-loving, possibly all-knowing, and definitely not all-powerful. God is far more powerful than any mere human, but his power is limited in some manner. The exact limits of his power are unknown; he can take action in some situations but not others.
This is much easier to work with. Now, every time an infant dies you can say that God wanted to help, but he couldn’t help, because of the mysterious limits on his power. And when a sickly infant recovers from a disease, you can say that God was able to help in that situation, and did so.
Perhaps this limitation comes in the form of a Devil, who has roughly the same amount power as God. (This is neat because you can grant God an “infinite” amount of power, only to be a opposed by a “similarly infinite” Devil.) The two of them are constantly at war with each other, trying to make the world better or worse. Humans are in the middle, and each person can exercise their own Free Will to assist either God or the Devil at any moment.
A perfect God would be wonderful, I’m sure. But considering the world that we live in, a limited God just makes more sense.
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(post updated 16 May 2012)