Philippians 4:6-7 "Do not be anxious about anything, but in everything ... present your requests to God. And the peace of God ... will guard your hearts and your minds in Christ Jesus."
What the apostle is doing here in effect is writing a prescription for one of our commonest ailments: worry. It's a remedy God recommends in Scripture in dozens of places. It's really effective, but so often we just don't use it -- we don't even try.