He writes that his joy is permanent (closing Philippians 1:18). The reason for Paul’s joy is that he knows that all this (everything that has happened to him) leads to his salvation. By salvation Paul does not refer to being saved from prison, but to being saved by God forever. It is likely that he is quoting a verse from the book of Job (in the Greek translation of the OT) here. In Job 13:16 Job exclaims, This will be my salvation. It is not the circumstances in themselves that lead to Paul’s salvation. The positive effect comes through the prayer of the church and the help of the Spirit, who is called here the Spirit of Jesus Christ.