do not be anxious about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God. And the peace of God, which surpasses all understanding, will guard your hearts and your minds in Christ Jesus. (Philippians 4:6–7 ESV)
Peace is not only the absence of conflict, but also the positive blessing of being in a right covenantal relationship with God through Christ. When this relationship is real and not imaginary, the peace of God surpasses human understanding and acts as a guard around our heart and mind. This guarded peace is perfect, and can be sustained when the person who is guarded keeps their mind stayed on the Lord (Isaiah 26:3), the trustworthy King. Therefore, we are not to be anxious about anything. And every request we have is to be brought before our King through prayer and supplication.
I think one of the keys to this peace is in that powerful word thanksgiving. We are always to be a thankful people. Not a superficial, smiley denial of conflict or pain; but rather a prayerful trusting upon the sovereign Lord who is for me and not against me. It was displayed for me in perfection last week through my beloved wife when she said after the death of our daughter Mercy; “I have never been so broken and thankful in all of my life.” This is a true child of the King who is being kept in perfect peace in the midst of conflict, anguish, and pain. This is a woman who is in a right covenantal relationship with God through Christ. She has the peace of Christ that surpasses all understanding.
You keep him in perfect peace whose mind is stayed on you, because he trusts in you. (Isaiah 26:3 ESV)