In Judgment, Soul Harness is an early game Ritual. It is the first ritual you can learn and unlock that can be cast via the Dark Altar.
As the time to cast the ritual is shorter than the ritual duration, it is technically possible to keep it consistently without much trouble, as long as you can sustain the material cost.
Soul Harness, as its name suggests, harness the very souls of your survivors. As their souls feed the altar, their own needs are neglected. For the duration of the ritual (960), your survivors will grow hungry at 70% of the usual rate.
This ritual can be useful to overall reduce the strain on your farms and economy if your survivors are becoming too hungry, but it is also a way for you to manage to obtain multiple food type bonuses with greater ease.