Matthew Poole and continuators on Exodus 32:5

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

(i. e.) Observed with what applause they received it and with what fury and resolution they prosecuted their former desire, he was born down with the stream, and, as it is probable, by the peoples instigation built an altar to it.

Heb. to Iehovah. Which title being peculiar to the true God, and being here given by Aaron to the calf with the approbation of the people, makes it more than probable that the people designed to worship the true God in this calf, which they made onely as a visible token of Gods presence with them, and an image by which they might convey their worship to God.