The fundamental framework for all of Paul’s theologizing, especially for “salvation in Christ,” is his eschatological understanding of present existence – as both “already” and “not yet.” With the resurrection of Christ and the gift of the promised Holy Spirit, God has already set the future inexorably in motion; thus salvation is “already.” But the consummation of salvation awaits the (now second) coming of Christ – the “Day of Christ,” Paul calls it (1:6, 10; 2:16); thus salvation has “not yet” been fully realized. The fact that the future has already begun with the coming of God himself (through Christ and the Spirit) means two crucial things for Paul: that the consummation is absolutely guaranteed, and that present existence is therefore altogether determined by this reality. That is, one’s life in the present is not conditioned or determined by present exigencies, but by the singular reality that God’s people belong to the future that has already come present. Marked by Christ’s death and resurrection and identified as God’s people by the gift of the Spirit, they live the life of the future in the present, determined by its values and perspective, no matter what their present circumstances.
Gordon Fee, Paul’s Letter to the Philippians, 50-51.