Many are troubled by "work out your salvation with fear and trembling." Paul is not denying grace (the hymn) or teaching salvation earned by good works or trying to scare them. "Fear..." means knowing that the living God is really present, not an abstraction. "Work out..." Paul or another teacher can't always be with them. Every believer has to come face to face with God in Jesus and open their life to God's work. But then God truly does work (1:6). We're never alone struggling with our own broken strength.
When the Gospel shapes our lives, we become part of God's ongoing self-revelation. God's children learning and practicing God's generous love and self-giving service in a twisted, selfish generation. Life is lit up and shines in the world giving a "word of Life" to others.