It is not our own peace that is here referred to. It is the peace of God—the peace which comes to us from a realization of God’s power and goodness and willingness to hold us by His right band as His children. The thought is that this peace stands guard continually, as a sentinel, to challenge every hostile or worrying thought or fear. It keeps the Christian’s mind so that he at heart has peace with the Lord, fellowship, communion; and it guards his mind also, his reasoning faculties, instructing him and assuring him respecting the Divine power and wisdom and love.