1 Peter 1:13

So prepare your minds for action, be completely sober (in spirit- steadfast, self-disciplined, spiritually and morally alert) fix your hope completely on the grace (of God) that is coming to you when Jesus Christ is revealed.

The mind should not be allowed to wander or think about just anything. All thoughts that come to mind need to be judged and cast down when they do not align with God’s word. When we manage our thoughts, we keep ourselves out of trouble and our spirits alert and sober.