Roman religion, with its lawyer's soul, made explicit the structure that votive practice everywhere assumes: do ut des, I give so that you may give. The votum was a formal, conditional promise, if you bring the fleet home, if the fever leaves my son, then I will dedicate the silver lamp, build the shrine, sacrifice the white heifer, and its fulfillment was a debt. The dedicant who received the favor was voti reus, liable under the vow, until payment; inscriptions across the empire close with the satisfied formula VSLM, votum solvit libens merito, the vow paid willingly and deservedly.
Strip the Latin and the structure appears on every continent: the Greek peasant promising a goat to Asclepius, the medieval sailor vowing a pilgrimage in the storm, the Mexican mother promising the Virgin a painted retablo, the Hindu devotee vowing a coconut, a tonsure or a crawled circumambulation if the examination is passed. Theologians in several traditions have squirmed at the apparent commerce, and mystics have insisted the divine cannot be contracted; the practice has ignored them serenely, because the vow does something subtler than purchase. It binds a moment of desperation into a relationship: the request is framed as the opening of an exchange, the favor as a gift that creates obligation, and the payment as public acknowledgment that the obligation was real. What looks like a contract is, anthropologically, reciprocity, the oldest social glue there is, extended upward.