"I can do all this through him who gives me strength." (Philippians 4:13)
Rejoice in the Lord always. Paul repeats it: again I will say, rejoice. Let your gentleness be evident to all. The Lord is near. Do not be anxious about anything, but in every situation, by prayer and petition, with thanksgiving, present your requests to God. And the peace of God, which transcends all understanding, will guard your hearts and your minds in Christ Jesus. The Catechism identifies this as the programme of Christian prayer in the face of anxiety: bring everything to God with thanksgiving, and receive in return not necessarily the answer you asked for but the peace that stands guard over the heart regardless of the answer (CCC 2633).
Finally, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable, if anything is excellent or praiseworthy, think about such things. The discipline of the mind is an act of worship: what we choose to dwell on shapes what we become. Paul's instruction is not to ignore evil but to fill the mind so completely with what is excellent and praiseworthy that there is less room for what corrupts.
Paul has learned to be content in all circumstances, whether well fed or hungry, whether living in plenty or in want. I can do all this through him who gives me strength. The verse is often extracted from context and used as a general confidence booster. In context it is a statement about contentment: Paul can endure every condition, abundant or deprived, because Christ strengthens him in each. The Catechism identifies Christian contentment as a participation in the divine sufficiency: the one who has Christ has enough, in every circumstance (CCC 2550).
Brothers and sisters, the peace of God that transcends all understanding is given in exchange for the anxiety you bring to him in prayer. You do not receive it by being calm enough to deserve it. You receive it by bringing the anxiety to God, with thanksgiving even for what you do not yet understand, and trusting him with it. The transaction is simple. The anxiety is real. Bring it. The peace that passes understanding is waiting on the other side of prayer.
Lord God, in everything by prayer and petition with thanksgiving we present our requests to you. Guard our hearts and minds with your peace that transcends all understanding. Teach us contentment in every circumstance through Christ who strengthens us. And fill our minds with all that is true and noble and right and pure and lovely. Through Christ our Lord. Amen.