The speaker imagines himself as a pawn on a chessboard, lying there like a blob of mercury: formless, passive, ready to be shaped by whatever fate decides. When the earth trembles, he slithers sluggishly from one square to the next. When the wind blasts, he slides from PQ2 to PQ4, a standard chess move, though he seems to make it because he is pushed, not because he chooses. Each disaster is stronger than the last, and each time he simply goes along with it.
The final stanza changes things. Fire burns the board, yet he stays "untouched," watching. That detail suggests a strange calm, maybe detachment, maybe a quiet kind of endurance. The mood is resigned and fatalistic, but it isn't panicked. The title's "I" matters here: the speaker is the pawn, and the board is life itself. The poem seems to say that we are moved by forces we can't control, yet some part of us can still stand back and watch.