Philppians 4:5b-6
[stand firm thus in the Lord (v1b)]... The Lord is at hand; 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 understanding, will guard your hearts and minds in Christ Jesus.
The person who s not standing firm in the Lord is anxious - everything depends on them, how can they make sure this turns out alright? I must control this, what about this thing that I can't control. The person standing firm in the Lord knows that God is at hand, he is near. the person standing firm in the Lord knows that we are not in control, but God is, and he can be trusted. The anxious person gets stressed when something goes wrong, running it over and over in their mind - praying to themselves, but still unable to do anything about it. The Christian reacts by praying to God, the person who can do something about it. The anxious person is assuming that they know best. The Christian knows that God actually does know best. The anxious person doesn't know if they can trust someone else to do what they're supposed to do. The Christian knows that God can be trusted. So, through prayer, God gives us peace. that peace surpasses understanding because the situation may not have change, the circumstances may be terrible, but the source of our peace is not crcumstances, it is tthe fact that God is near to us.