The central image of the poem is the mask itself.  Dunbar describes, "We wear the mask that grins and lies," hinting that the mask appears joyful to hide something sad or angry underneath.  It grins to hide the true emotions of the wearer.  

In the second verse, the wearers of the masks almost sarcastically or bitterly say, "Why should the world be over-wise, In counting all our tears and sighs?" as though the world does not need to be burdened with their misery.  However, under the mask, "We smile, but, O great Christ, our cries to thee from tortured souls arise."  The wearers are in pain, but this is hidden by the mask.

Literally, the masks hide faces, emotions, and fears.  The mask hides the pain of people who do not want others to see their pain.  The mask is also a metaphor for the pain and repression that black Americans felt at the beginning of the 1900s, and throughout the century.  They felt that they had to smile to hide how they really felt about their circumstances, because their situation seemed hopeless and no one would listen or help them.