What does Philippians 1:6 mean?

Paul begins this verse with a statement of great confidence in the Philippian Christians. While salvation from the penalty of sin happens at the moment a person accepts Christ, the process of becoming more like Christ is exactly that: a process. Paul is completely sure that this "sanctification" will continue in the lives of these believers. In particular, this assurance is grounded in the work of Jesus Christ. In other words, Paul has no doubts about their salvation and their faithful service to Christ.

The "day of Jesus Christ" clearly speaks of the end times, but interpreters debate other specifics related to this reference. Some see this as an allusion to the rapture, which will take place at any moment (1 Corinthians 15:50–58; 1 Thessalonians 4:13–18). Others see this statement as a mention of the end of the seven–year tribulation period just prior to the millennium (Revelation 19—20). A third possibility is that Paul was not referring to any specific date or time, but simply focused on the good things that would take place when these believers met Christ in the future.