“Delight yourselves in the Lord; yes, find your joy in Him at all times.” Philippians 4:4
Misery is optional even though pain and suffering are inevitable. Those words were written by a man who lives with excruciating pain every day. How can misery be optional for someone in pain? How is it Paul mentions joy 17 times in a short letter he wrote from prison?
For those who experience and express the fruit of the Holy Spirit, who have a relationship with the risen, living Christ, there is a joy that is not controlled by circumstances.
The peace Paul experienced and prescribes for you and me can be called the peace that doesn’t make sense. It is a peace that “transcends all understanding.” (Philippians 4:7) The joy of which Paul writes can be called the happiness that doesn’t make sense. This is true because this peace and joy are the fruit and evidence of the Holy Spirit Who lives in us.
This peace and joy are not controlled by our circumstances.
What is the foundation of that peace and joy? According to Paul, that foundation is the Lord Jesus Christ. We are to delight ourselves in the Lord and find our joy in Him at all times.
What is the foundation of your serenity and joy?
When Paul writes his words about joy, he directs us here to a foundation for serenity and joy that is not fragile: “Delight yourselves in the Lord; yes, find your joy in Him at all times.”
Dick Woodward, Marketplace Disciples (p. 188-190)
4SpiritualSecrets 
Great