What does it mean to say God is jealous (Heb. qanna’)? In a recent JBL piece, Nissim Amzallag points out that it is intimately linked to Yahweh’s fieriness (cf. Psalm 79:5; Ezekiel 38:19) and to “furnace remelting.” If there is a hint of volcanic power in the Old Testament uses of the term, it remains that “the only gods specifically associated with volcanoes in antiquity are the gods of metallurgy” (240).
The symbolic associations of remelting are powerfully evocative: “The strong reducing power of furnaces induces a whole reduction of copper oxides . . . so that furnace remelting produces a complete regeneration of the metal, without any loss of matter. From a symbolic perspective, furnace remelting is a process of rejuvenation by fire of the cauldron: this cultic artifact was identified in antiquity both with the furnace and with the mouth of a volcano.” For the ancients, “furnace remelting was the only process . . . that made possible such a rejuvenation of matter” (241).
Yahweh possesses the power of rejuvenating matter as an essential attribute. Amzallag runs through the signs that Yahweh gives Moses on Sinai – scepter to serpent and back, healing of leprosy, water to blood – and concludes that “the three wonders express a unique reality: the process of rejuvenation inherent in furnace remelting (first wonder), its extension to healing (second miracle), and even to vitalization of the entire universe (third wonder)” (245).
Amzallag runs through various passages that link Yahweh’s fiery, remelting qanna’ with His holiness, noting, for instance, that “the destructive dimension of YHWH’s holiness is confirmed by the use of herem in the Bible to designate consecration by total destruction” (249). He also notes passages where the “day of Yahweh” is a day of volcanic activity, which is to say, a day when the fiery presence of God remelts and remakes the entire cosmos.
In short, “the concepts inspired by the process of furnace remelting seem to be of central importance in biblical theology. They promote the belief that the necessary outcome of a tragic event is the recovery of an improved state, the one closest to the ‘revitalized origin.’ They also condition the vision of the final issue as an ultimate remelting event bringing back an entirely renewed earth” (252).
(Amzallag, “Furnace Remelting as the Expression of YHWH’s Holiness: Evidence from the meaning of qanna’ in the Divine Context,” JBL 134:2  233-252.)