And he took the calf which they had made, and burnt it in the fire, and ground it to powder, and strawed it upon the water, and made the children of Israel {i} drink of it.

(i) Partly to despise them for their idolatry, and partly so they would have no opportunity to remember the calf later.

Wesley's Notes

32:20 He burnt the calf - Melted it down, and then filed it to dust; and that the powder to which it was reduced might he taken notice of throughout the camp, he strawed it upon the water which they all drank of. That it might appear that an idol is nothing in the world, he reduced this to atoms, that it might be as near nothing as could be.

Jamieson-Fausset-Brown Bible Commentary

20. he took the calf which they had made, and burnt it in the fire, &c.-It has been supposed that the gold was dissolved by natron or some chemical substance. But there is no mention of solubility here, or in De 9:21; it was "burned in the fire," to cast it into ingots of suitable size for the operations which follow-"grounded to powder"; the powder of malleable metals can be ground so fine as to resemble dust from the wings of a moth or butterfly; and these dust particles will float in water for hours, and in a running stream for days. These operations of grinding were intended to show contempt for such worthless gods, and the Israelites would be made to remember the humiliating lesson by the state of the water they had drunk for a time [Napier]. Others think that as the idolatrous festivals were usually ended with great use of sweet wine, the nauseous draught of the gold dust would be a severe punishment (compare 2Ki 23:6, 15; 2Ch 15:16; 34:7).

Matthew Henry's Concise Commentary

32:15-20 What a change it is, to come down from the mount of communion with God, to converse with a wicked world. In God we see nothing but what is pure and pleasing; in the world nothing but what is sinful and provoking. That it might appear an idol is nothing in the world, Moses ground the calf to dust. Mixing this powder with their drink, signified that the backslider in heart should be filled with his own ways.