How often a human heart sighs 'Oh, that I could properly guard my thought-life!' The thoughts are so unruly. One never knows when they may suddenly run riot. These riotous thoughts can be guarded by the peace of God, a power. It is the absence of peace in the heart which causes one's thoughts to be restless. But the peace of God is like a protective shield around the believer's heart and thoughts. For this peace surpasses all understanding.