Deuteronomy 9:12

And the Lord said unto me
The omniscient God, who knew what was doing in the camp of Israel, though Moses did not, of which he informs him:

arise, get thee down quickly from hence;
from the mount where he was; and the word "arise" does not suppose him to be sitting or lying along, neither of which postures would have been suitable, considering in whose presence he was; but is only expressive of urgency and haste of his departure; it is not used in ( Exodus 32:7 )

for thy people, which thou hast brought forth out of Egypt, have
corrupted themselves;
their way, as the Targum of Jonathan; that is, by idolatry, than which nothing is more corrupting and defiling; the Lord calls them not his people, but the people of Moses, being highly displeased with them; and ascribes their coming out of Egypt to Moses the instrument, and not to himself, as if he repented of bringing them from thence:

they are quickly turned aside out of the way which I commanded them:
it being but about six weeks ago, that the command forbidding idolatry, the sin they had fallen into, had been given them:

and they have made them a molten image;
the image of a calf made of melted gold.