Observation: This text takes place right after one of my favorite texts from the whole New Testament: the Christ Hymn, which tells the story of Jesus, who was in the form of God, humbling himself and even dying on a cross so that he would be exalted in all the earth. In these next few verses, Paul gives his readers the "application." Because this amazing thing has happened in Jesus, we can "work out our own salvation with fear and trembling." This doesn't mean to "save" ourselves--Paul just laid out how Jesus did that--but to work out the meaning of the cross and resurrection in our own lives, and let it affect the way we think and act. It will look different for different people, but trust that "God is at work in you."
Application: I guess the "fear and trembling" part makes sense, because, as Paul has laid out, we are truly free in Christ. There is no one cookie cutter way of life for every Christian: we work out the meaning of Jesus in our own lives, in our own time. Sure, Christians who are taking this seriously will all strive to love one another, and to imitate Jesus in healing, inclusion and justice. But that still provides a LOT of latitude for you and me to work this thing out in the way that makes most sense for us. It would be totally confounding for me, and I'd never know if anything I'm doing is right, except for the promise in the next verse: "God is at work in you, enabling you both to will and to work for his good pleasure."
Prayer: Dear Holy Spirit, please work in me as I work out this life of faith. Amen.