Devouring Souls should be the wrong word, instead, the word he should have used was, respite.
The Souls of the realm come to him to find rest. The voiceless multitude who did not know the weight they carried had finally found a home.
When he was a Soul Seizer or a Soul Reaver, then he was indeed consuming Souls, but after gaining the bloodline of Sheol and giving birth to the Will of Souls, thereby acquiring the Gates of Purgatory and Ambrosia as his Aether, which all led to him having the ability to house Soul Origin, he no longer devoured souls, instead as a means of payment, souls come into his domain for rest and they give him the energy they had gathered throughout their lives.