"What is filth? Why do you feel it's filthy? There is nothing in it, how is it any different from all the exquisite food and drink you have seen in the world?"
"But why don't we eat those exquisite foods and drinks?"
"Because at this moment, you feel they are filthy. You are still attached to appearances, so this is your Cultivation. When you no longer find it filthy but truly enjoy it as you would delicious food and drink, you will no longer be attached to appearances."
"... But disciple doesn't understand, why do we have to eat human corpses?"
"Because… only the bodies of people can bear countless sufferings and sins. By consuming it, you take on their karma, endure their suffering, and the suffering in the world is constant. If we bear a bit more of it, people in the world will bear a little less, and thus we will be one step closer to becoming Buddhas..."