The flow of the souls of the dead from the Material planes into the Outer (God) planes, as determined by their faith and conduct
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Deities and powers of good are enhanced by, and care for, the souls of their faithful and deserving followers once they arrive on those powers' home planes. Demons, devils and suchlike revel in the torment and feed on the essence of the souls damned into their hands by their evil lives. Collectively, this acquiring of souls by the Powers is referred to as the Soul Harvest.
By and large, the powers of Good will not interfere with the passage of souls to each others' domains, but the demons and devils will - and do - steal and deceive souls from their proper paths into their own clutches. In addition, the fiends fight eternally between themselves for the right to claim all the souls of the damned, a struggle known as the Blood War.