NOTE: This is a condensed excerpt from my forthcoming (2014) commentary on Philippians.
Here in 1:5-6 we have the past, present and future of our salvation in short span. Paul speaks of “the first day” the Philippians believed the gospel and became partakers of it and its benefits (1:5). He then speaks of the “present time” during which the Philippians live, during which they are experiencing fellowship in the gospel and the ongoing work of God in/among them (1:5-6). And he concludes by speaking the “day of Christ Jesus” when all of God’s purposes will reach their consummation (1:6). On that day “every knee should bow, in heaven and on earth and under the earth, 11 and every tongue confess that Jesus Christ is Lord, to the glory of God the Father” (Phil 2:10-11). It is these temporal references that help the Philippians form a frame of reference for all that God has done and is yet to do.
What was true of the Philippians is true of us as believers today. God is the one who began the great work of redemption in us, making us a new creation by the work of his Spirit. He continues that work in us as we share in the benefits and implications of the gospel in fellowship with other believers. But we still must await the great day of Christ for that work to be completed by the transformation of our lowly bodies into conformity with the glorious body of the risen Jesus (Phil 3:20-21).