John Calvin Commentary Exodus 32:20

"And he took the calf which they had made, and burnt it with fire, and ground it to powder, and strewed it upon the water, and made the children of Israel drink of it." — Exodus 32:20 (ASV)

And he took the calf which they had made. It might seem to be a cruel and inhuman punishment that Moses should, in a way, infect the bowels of the people with the corruption of the crime. They had already polluted both their bodies and souls more than enough, without the contagion entering any deeper.

Besides, he was thus likely to drive them to despair, as they bore within them the reason for their condemnation, just as a woman nourishes her offspring in the womb. Nevertheless, this was the remedy to be applied to their senselessness. For, however they might have been terrified for a moment, the memory of their crime and their fear of punishment would have immediately vanished if this mark of their defilement had not been thoroughly impressed upon them.

This, then, was a kind of cautery, by which they might feel that the disgrace of such foul idolatry not only clung to their skin but was fixed deep in their very bowels.

For in this way also their shame was driven home to them when they took the substance of their god into their stomachs, only to soon afterward expel it with their excrement. Therefore, they were compelled to drink and to expel a part of their god, so that their superstition might be all the more offensive to them.

Besides, if the ashes had been scattered on the ground, there was a danger that some of the more obstinate people might collect the relics. This evil was prevented when the gold from which the false god was melted was mixed with dung.

Finally, Moses is said to have made them drink the accursed water, not because he himself handed the cup to each of them, but because the dust was thrown into the stream from which they all drank, as is stated in Deuteronomy 9:21.