No sacrifice lands in a vacuum. When a man lays his time, his attention, his loyalty on some altar, he feeds whatever sits there, and the thing he feeds grows strong enough to shape him back. The pagan thought he served nothing. He served the appetite he had enthroned.
Whatever you commune with, you become. Sit down at the table of resentment or contempt often enough and you take on their character, because participation is never neutral. The warning is blunt. Aim your devotion at the highest thing you can conceive, or you will worship something lower without noticing.