Charles Spurgeon Commentary Exodus 32:5

"And when Aaron saw [this], he built an altar before it; and Aaron made proclamation, and said, To-morrow shall be a feast to Jehovah." — Exodus 32:5 (ASV)

And when Aaron saw it, he built an altar before it; and Aaron made proclamation, and said, Tomorrow is a feast to the LORD.

"To Jehovah." They intended to worship Jehovah under the form of a bull – the image of strength. Other idolaters go further, and worship Baal and various false gods, but, between the worship of a golden calf and the worship of false gods, there is very little choice; and, between the idolatry of the heathen and Popery, there is about as much difference as there is between six and half a dozen.

And when Aaron saw it, he built an altar before it; and Aaron made proclamation, and said, Tomorrow is a feast to the LORD.

They were going to worship Jehovah under the emblem of an ox. This is what you will hear idolaters say; they do not worship the image, they say, but the true God under that image. Yet that is expressly forbidden under the second commandment.