Is this story about "faithfulness" or "faithlessness"?

Well, it depends on your perspective. The actual Gospel Project title for this session was "Faithlessness", and certainly that is true in relation to the people of Israel. However, this is also a story of "faithfulness" in relation to God. Idolatry is the distortion of worship of God, which leads to the deserved judgment of God. The Good News, however, is that God is gracious, and we need to depend on the grace of God, period.