Rejoice in the Lord always; again I will say, rejoice. Let your reasonableness be known to everyone. 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 all understanding, will guard your hearts and your minds in Christ Jesus.
Finally, brothers, whatever is true, whatever is honorable, whatever is just, whatever is pure, whatever is lovely, whatever is commendable, if there is any excellence, if there is anything worthy of praise, think about these things. Philippians 4:4-8 (ESV)
The apostle Paul didn’t have a lot of worldly stability in his life, to put it mildly. On the surface he didn’t have a whole lot to rejoice about. Being stoned (with rocks,) beaten, flogged, starved, shipwrecked and put in prison isn’t exactly what most people would call a good time.
Most of the time, Paul had nothing as far as material wealth. He had little if any assurance of physical safety, but in Christ, Paul had everything.
The human condition is such that there is no permanent home in these imperfect bodies and in this flawed and broken world. If we put our trust in our health, or our family and friends, or in our abilities, or in our wealth, we are trusting in things that cannot last and are temporary at best. Only Jesus offers us the peace of knowing that in Him we have life forever, life without end.
No matter what this life throws at us, this life is not all there is.
As the apostle Paul wrote in his letter to the Galatians:
I have been crucified with Christ. It is no longer I who live, but Christ who lives in me. And the life I now live in the flesh I live by faith in the Son of God, who loved me and gave himself for me. Galatians 2:20 (ESV)
We have peace because we know to whom we belong.