The images of suffering and being oppressed are some of the most powerful ones that add meaning to Plath's poem.  The opening image of the "black shoe" compressing and forcing a foot to conform to it is an image in which one gets the idea that there is suffering in terms of how suffocation can feel.  The "ghastly statue" is another image that reflects how powerful and overwhelming the conditions of repression can be in one's life.  Plath pivots from this to the image of the Jewish victim in the Holocaust, imagery that collapses the personal and political into one vision of repressive purgatory from which escape is impossible:

A Jew to Dachau, Auschwitz, Belsen./ I began to talk like a Jew./ I think I may well be a Jew.

The preceding image of the train taking victims of Holocaust to their death is one in which one fully understands how repressive Plath feels in her life and what it means to deal with the overwhelming externalities that define being in the world.  These images help to enhance the meaning of the poem because they bring into focus the difficulties and pain that Plath must endure.  They help to bring clarity to what it is that Plath detests and what it is that she has borne for far too long.  In being able to articulate images that represent oppression, there is little doubt in what Plath wishes to articulate and emphasize.  These images help to construct a narrative where suffering becomes an intrinsic part of the modern setting and understanding its role becomes essential to finding any semblance of happiness.