And to my mind the answer is that God does not demand it.

It is Man who demands it.

It is the instinctive craving of the human soul for _certainty_ that requires a demonstration so convincing as to leave no room for doubt of our perfectly happy relation to the Supreme Spirit, and consequently to all that flows from it, whether on the side of the visible or of the invisible.
When we grasp the fact that such a standpoint of certainty is the necessary foundation for the building up in ourselves of the Divine Ideal then it becomes clear that to afford us this firm basis is the greatest work that the Spirit, in its relation to human personality, could do.
We are often told that the offering of sacrifices had its origin in primitive man's conception of his gods as beings which required to be propitiated so as to induce them to do good or abstain from doing harm; and very likely this was the case.

The truth at the back of this conception is the feeling that there is a higher power upon which man is dependent; and the error is in supposing that this power is limited by an individuality which can be enriched by selling its good offices, or which blackmails you by threats.

In either case it wants to get something out of you, and from this it follows that its own power of supplying its own wants must be limited, otherwise it would not require to be kept in good temper by gifts.
In very undeveloped minds such a conception results in the idea of numerous gods, each having, so to say, his own particular line of business; and the furthest advance this mode of thought is capable of is the reduction of these various deities to two antagonistic powers of Good and of Evil.