How does Mariama Ba use imagery in So Long a Letter?

Imagery:

Teachers – at kindergarten level – as at university level – form a noble army accomplishing daily feats, never praised, never decorated. An army forever on the move, forever vigilant. An army without drums, without gleaming uniforms. This army, thwarting traps and snares, everywhere plants the flag of knowledge and morality.

Mawdo, man is one: greatness and animal fused together. None of his acts is pure charity. None is pure bestiality.