The "rereward" of the armies of ancient Bible times was assigned the same task as is the rearguard of modern warfare. It protected the army from dangerous rear attacks while it was pressing forward to victory.
To the exalted thought of Isaiah, the "rereward" was essentially spiritual. He recognized men's complete defense from evil to be above mere, unreliable human effort, for he joyously declared, "Thy righteousness shall go before thee; the glory of the Lord shall be thy rereward" (58:8).
A fundamental point in Christian Science is that the human consciousness must be redeemed. That is, every misconception of life, truth, intelligence, and substance as existing in matter must be exchanged for the absolute understanding of life, truth, intelligence, and substance in Spirit, God. Thus as students of Christian Science we are waging a war with materiality. How strengthening and comforting, then, to know that our righteousness is going before us! Our "rereward" is the omnipotence, omniscience, and omnipresence of divine Love, revealed by Christ, Truth, and our understanding of Love's allness wipes out the false beliefs of an unrighteous past which would rob us of spiritual victory.