How could Paul write 'Rejoice evermore' in Philippians?

Les teaches that Philippians is a precious little letter, chock full of the believer's experience, and that in spite of adversity the man could write, 'Rejoice, evermore I say, Rejoice.' He says that rejoicing is the whole theme of Philippians. Les also explains that Paul writes to the church at Philippi, urging believers to follow him as he follows Christ—not the Jesus of Nazareth of the dusty roads of Palestine, but the crucified, risen Lord of glory. Paul's ability to rejoice rests on the risen Lord, not on easy circumstances.