Guard your mind from thoughts that will lead you the wrong way. The mind needs to be guarded from thoughts which bring confusion, anxiety, fear, and discouragement. You are what you think. Thoughts can defeat you. Thoughts may depress you. The wrong thoughts can easily confuse you. Those are reasons to guard your mind.
"And the peace of God . . . will guard your minds and hearts" (Philippians 4:7). Your mind will serve you well in making decisions, when you rely upon the peace of God. When peace is not found, it is a warning sign that you have gone astray. Every believer should walk in the peace of God. Peace is a fruit of the Holy Spirit. Your mind is renewed to know God's will by the Holy Spirit. Peace confirms it. Guard your mind with God's peace.
As a believer, recognize that you are in spiritual warfare. Your mind is the battle ground. All manner of thoughts will come your way. There will be thoughts of doubt, temptation, and confusion. Every thought that robs you of peace is not from God. Therefore, "bring every thought into captivity to the obedience of Christ" (2 Corinthians 10:5). Do that in prayer, as you guard your mind.
Feed your mind on the truth of God found in your Bible. Guard your mind with truth against the lies of the world. Peace always confirms the truth. Peace from God is a sure guard for your mind. "And let the peace of God rule in your hearts" (Colossians 3:15). Let God guard your mind with peace.