John Calvin Commentary Psalms 106:19

"They made a calf in Horeb, And worshipped a molten image." — Psalms 106:19 (ASV)

They made a calf. Here he represents their rebellion as extremely base, because they abandoned the true worship of God and made for themselves a calf. For although it was their intention to worship God in this manner, yet the prophet reprimands their brutal stupidity, because they worshipped before the molten image, and represented God by the figure of an ox which eateth grass. From this, the prophet infers that God had been robbed of His honor, and that all His glory had been tarnished.

And surely it is so; for although the idolaters pretend to serve God with great zeal, yet when, at the same time, they represent God to themselves as visible, they abandon the true God and impiously make for themselves an idol. But he reproaches them with being guilty of still greater impiety when he says, after the likeness of an ox that eateth grass; and contrasts with it their honor or glory. For since God had clothed them with His own glory, what madness was it to substitute in place of Him not only an ox, but the inanimate form of an ox, as if there were any resemblance between God who creates all kinds of food, and that stupid animal which feeds on grass?

However, it is necessary to observe the prophet's design, which is to point out that human blindness is all the more base and abominable because, not contenting themselves with any common form of superstition, but casting off all pretense, they give themselves up to the most shocking forms of worshipping God.

If the people had formed for themselves a likeness of God in the form of a man, even that would have been impiously robbing God of His due. How much more shameful was their conduct when they assimilated God to an ox? When men preserve their life by eating and drinking, they acknowledge how frail they are, because they derive from dead creatures the means of its continuation.

How much greater is the dishonor done to God when He is compared to brute beasts? Moreover, the comparison referred to increases the enormity of their guilt. For what honor was it for a holy people to worship the inanimate likeness of an ox instead of the true God? But God had condescended to spread out the overshadowing wings of His glory upon the children of Abraham, that He might bestow on them the highest honor. Therefore, in stripping themselves of this honor, they had exposed their own baseness to the derision of all the nations of the earth. And for this reason, Moses uses the phrase nakedness when he is describing that crime of idolatry:

And when Moses saw that the people were naked (for Aaron had made them naked unto their shame among their enemies) (Exodus 32:25).

If anyone is inclined to say that the ark of the covenant was a representation of God, my answer is that that symbol was given to the children of Israel, not to engross all their attention, but only for the purpose of assisting and directing them in the spiritual worship of God.