They had turned away from their Deliverer and Fashioner and God for some dumb, lifeless, impotent idol. And it wouldn't be the last time, either.
In today's reading from the Prophecy of Isaiah, there is more recollection of and exhortation against such a horrible idea, (Isaiah 2:17ff):
And the haughtiness of man shall be humbled, and the pride of men shall be brought low; and the Lord alone will be exalted in that day. And the idols shall utterly pass away. And men shall enter the caves of the rocks and the holes of the ground, from before the terror of the Lord, and from the glory of his majesty, when he rises to terrify the earth. In that day men will cast forth their idols of silver and their idols of gold, which they made for themselves to worship, to the moles and to the bats, to enter the caverns of the rocks and the clefts of the cliffs, from before the terror of the Lord, and from the glory of his majesty, when he rises to terrify the earth.
On that Terrible Day of the Lord, Judgment Day, "men will cast forth their idols of silver and their idols of gold which they made for themselves to worship...". On that day, our naked souls shall be confronted by the mighty omnipotence and holiness of God, and we idolaters (we don't so much actually fashion ourselves little gods to worship, but by the double whammy of neglecting to live as Christians and by giving our heart to some one or some thing besides the One, True God, we effectively have) will scatter like palmetto bugs (fancy southern way of saying 'big roaches') when the light comes on in the morning.
For us, it will not so much be a scattering of terror as if the Terminix man has arrived and we recognize him--as if God were coming to exterminate us, rather, the brightness of the light of God, the power of his presence, and the might of his holiness will cause us to drop to our knees and realize in that instant that "The Lord: he is God and has revealed himself to us!" We will want to scatter and cover up every idol and idolatrous action in our lives and "run to the caverns" as Isaiah says. By then, though, it may be too late to turn back. Shoulda-coulda-woulda is out of place and time on That Day.
Which is why we celebrate Great Lent: to see and remember the idolatry of others, and to recognize our own, so that we can "Turn and Live" as the Prophet Ezekiel says (Ezekiel 18:32).
Don't wait until tomorrow!
My soul, my soul, arise! Why are you sleeping? The end is at hand! Destruction hangs over you! Come again to your senses! That you may be spared by Christ our God, who is everywhere filling all things.
--Kontakion Tone 6, Great Canon of St Andrew of Crete