No other gods, and no graven images.  Idols are the things we chisel out with our minds to serve us; we want the ones that make no demands on us.  The first concern of the first two commandments is that we serve the God who is, not the one we make up.  We must be vigilant not to mis-shape God, to whittle Him down to our size, to reduce Him to what we can control.  The great sin of this is that we restrict the One who cannot be restricted; we reduce the One who is irreducible. Let God be who He is so He can shape us —rather than us shape Him. 

Deuteronomy 5:7–8a (ESV)

7“ ‘You shall have no other gods before me. 

8“ ‘You shall not make for yourself a carved image.