First, work out your salvation (12-13). God's good and wonderful purpose for us is to grow in the image of Christ. This is the life-long process of sanctification and it is something we can't do on our own. The desire and power for this comes from God as He works in our hearts through His Spirit and word. Our part is to cooperate! In light of Christ's example of obedience and exaltation, we are to work out our salvation with fear and trembling. How great was the price of our salvation and how wondrous the glory that awaits us! The grace and mercy of our Lord motivates us to obey His word and grow. Second, do everything without grumbling or arguing (14-18). God's vision for us is to shine like stars in this dark and wicked generation. For this, we are to be blameless and pure, which is impossible if we allow ourselves to grumble and argue with each other. Shining and complaining are complete opposites! The Holy Spirit is grieved when we struggle with each other. Instead, look at Paul's example. Even if his life was being poured out like a drink offering on the sacrifice and service of the Philippians' faith, he rejoiced. They were to rejoice as well, as God was using their obedience to produce the image of Christ in them.
Application: Father, help us to walk in the Spirit and to grow in Christ. Forgive our grumbling and arguing.
One Word: It is God who works in you!