It is one of the most comforting verses in all of the Bible. After receiving two imperatives from the Lord–“Be anxious for nothing” and “let your requests be made known unto God” (Phil. 4:6)–there is this promising reassurance, which 
has helped many of us to “go on” when we didn’t think that we could: “…and the peace of God, which surpasses all understanding, will guard your hearts and minds through Christ Jesus” (4:7).
We are promised that “the peace of God…will guard [our] hearts and minds.” Think about that for a moment. The Greek word for “guard” is a military term, which pictured soldiers standing on duty, guarding the city gate from the inside, protecting against the enemy. Can you see it?
It is time for Christians to stop carrying all of their “cares” (1 Pet. 5:7) and worrying all of their “worries” (Phil. 4:6), and it is time to allow God’s peace to garrison our hearts (emotions) and our minds (thoughts), so that we learn to trust Him and obey Him more every day!