He'd been arrested, held for 2 years in Caesarea, shipwrecked on his state-escorted trip to Rome by the prison authorities, stranded on the Island of Malta for 3 months, only to be rescued and taken to prison in Rome awaiting trial before Caesar. Paul is sitting in lockup. He's not free to visit the fellowship of Christ followers back in Philippi, even though they need him.
And now, in part of his letter to the church in Philippi, he lets them know that he is in chains, that he's facing critics, and that he's in the midst of crisis. So how do you think Paul is feeling? Paul says, "Because of this, I rejoice." (Philippians 1:18)
What? You rejoice? How can you feel joy in the midst of those circumstances? How can you rejoice when so much opposes you, and torments you, and separates you from direct contact with those of us you love and who agree with you? Paul answers, "The important thing is that in every way, Christ is preached."
And Christ was being preached, indeed. Because of his chains, Christ was being preached to Caesar's guards (Phil 1:13). Because of his critics, even with their false motives, Jesus was getting additional press (Phil 1:18). And even in his crisis, whichever way it went, it would turn out well for him in the name of Jesus Christ (Phil 1:21-22). Because of all this, Paul says, "Yes, and I will continue to rejoice."
Paul is able to do this because of his single mind. Outward circumstances mean nothing to the disciple, so long as Christ is exalted. Do you have it? Do you have the single mind that allows for joy in all circumstances? How you would fill in Paul's statement in Phil 1:21 - "For to me, to live is ________, and to die is ______."
To live is money, and to die is to lose it all? To live is power, and to die is powerlessness? To live is fame, and to die is to be forgotten? There is not joy in these.
Only in "To live is Christ, and to die is gain," will there be more joy.