In the closing chapter of Defensio Fidei Catholoicae: De Satisfactione Christi Adversus Faustum Socinum Senensem , Grotius provides a fascinating overview of sacrificial practices outside Israel. He moves from the classical world to India, the Americas, and the Canary Islands. He talks about animal and human sacrifice, and includes the “self-dedications of the Decii” under the heading of sacrifice (p. 265).
The argument takes a curious turn. Grotius begins the chapter arguing for the expiatory character of biblical sacrifice. He says that the biblical witness is sufficient, but then goes on to suggest that it will be helpful to survey sacrificial practice more widely: “the common notion of the nations, or rather a most ancient tradition diffused in all lands [can] explain somewhat more fully the nature of the expiatory sacrifice” (257).
By the end of the survey he is drawing theological conclusions from pagan practice: “this custom of the Gentiles of expiating sins by the slaughtering of men or cattle sheds considerably light on the very nature of expiatory sacrifices and the words proper to this argument” (267). Pagan sacrifice did not work the way Socinus says Christ’s sacrifice worked - by creating faith and so encouraging people to amend life. Rather, those pagan sacrifices were seen as substitutionary propitiations: “lustral or expiatory rituals served to placate the divine power ( ad placandum numen ), and so to obtain impunity for previously committed sins” (261).
Grotius does go on to argue that biblical sacrifices have the same effect, but the prominence of pagan sacrifice in the argument is remarkable.