In the letter to the Philippians, the apostle Paul speaks of joy 16 times - more than in any of his other letters. Remarkably this letter was written from Rome where Paul was detained under house arrest. In other words, he didn't write about joy because his circumstances were going well.
Imagine what life could be like if you could know joy as the steady current of your soul regardless of your circumstances. How could this be possible? Only if your perspective of life, the vision for your life, was not "situation based" or "circumstance based" but "relationship with Christ" based. And here is the secret to Paul's joy. His vision and aspiration for life is found in Philippians 3:10. "I want to know Christ and the power of his resurrection and the fellowship of his sufferings." (paraphrased). If this were the vision of our lives, joy would be possible because all circumstances can enable us to know Christ, the power of his resurrection and the fellowship of his sufferings.
In other words, this is a vision of life that is "unshakable" because it is not "circumstances driven." It is not based on what I believe my life could or should look like. It is not based on any sense of "the life I deserve." For Paul, the purpose of his life and the future picture he sees for it is "to know Christ and the power of his resurrection and the fellowship of his sufferings." That's what he wants his life to be about.
The circumstances of your future, which you envision and hope for, may or may not materialize. But knowing Christ and the power of his resurrection and the fellowship of his sufferings, is a "circumstances-less" vision. It is "beyond circumstances." It means if my circumstances are going great, I can celebrate this with Christ in a daily relationship of his companionship. More profoundly, if my circumstances are difficult, I can grow deep in the fellowship of Christ, in his comfort and hope, his power and presence.
Consistent with this is that we see in Philippians that Paul mentions "Christ" 39 times. There's the real insight. His joy (mentioned 16 times) is the result of his passion for Christ (mentioned 39 times). The point is, he is a person who sees his life, and lives his life through Jesus - regardless of his circumstances and this is the secret to his joy. He is Jesus focused in vision, he is Jesus grounded in daily life. So joy overflows in the letter because the word Christ overflows in the letter.
One of the hallmark statements of Philippians is Paul's breathtaking announcement that "for me, to live is Christ and to die is gain." If we're honest, hardly any of us could say "to die is gain." But for Paul, death means "going to be with Christ." (there's the Christ centered relational vision again). So you might be thinking, "I'd like to be able to say "to die is gain."" But you and I could never say this and mean it, unless we had come to the place of fully embracing "to live is Christ." (vs. "to live is to be happily married" or "to live is to have a big job and make a lot of money." You get the point.)
Finally, Paul didn't arrive at this level of depth overnight. He got there over years of life with Jesus; years that included many excruciating hardships. He mentions these in 1 Corinthians 11. See, our roots in Christ grow deep when fertilized with hardship. No amount of Bible studies or small groups can get us to this same level of depth and maturity. This means there are many benefits to hardship. In closing, I'll recap with "10 Benefits of Hardship" (from sermon at Hope Church on January 12, 2013).
Hardship clarifies what’s
important
Hardship frees us from pursuing
the trivial and missing the point in life
Hardship frees us from worrying
about what others think
Hardship grows our compassion
Hardship changes our purpose
Hardship changes our big picture
perspective
Hardship cuts the garbage out of
our religion
Hardship helps us experience what’s
meaningful in life
Hardship deepens and matures us as
people
Hardship teaches us we can trust
God