Answer: The following scripture and commentary explains the reformed perspective:
“Which I commanded them not, and which never came to my mind” (Jeremiah 7:31)
This reason ought to be carefully noticed, for God here cuts off from men every occasion for making evasions, since he condemns by this one phrase, “I have not commanded them,” whatever the Jews devised.
There is then no other argument needed to condemn superstitions, than that they are not commanded by God: for when men allow themselves to worship God according to their own fancies, and attend not to his commands, they pervert true religion.
And if this principle was adopted by the Papists, all those fictitious modes of worship, in which they absurdly exercise themselves, would fall to the ground.
It is indeed a horrible thing for the Papists to seek to discharge their duties towards God by performing their own superstitions. There is an immense number of them, as it is well known, and as it manifestly appears.
Were they to admit this principle, that we cannot rightly worship God except by obeying his word, they would be delivered from their deep abyss of error.
The Prophet’s words then are very important, when he says, that God had commanded no such thing, and that it never came to his mind; as though he had said, that men assume too much wisdom, when they devise what he never required, nay, what he never knew.
It is indeed certain, that there was nothing hid from God, even before it was done: but God here assumes the character of man, as though he had said, that what the Jews devised was unknown to him, as his own law was sufficient.
Answered by John Calvin (1509-1564) in his Commentary on Jeremiah