The reading is from St. Paul's Letter to the Philippians 2:12-15

Brethren, as you have always obeyed, so now, not only as in my presence but much more in my absence, work out your own salvation with fear and trembling; for God is at work in you, both to will and to work for his good pleasure. Do all things without grumbling or questioning, that you may be blameless and innocent, children of God without blemish in the midst of a crooked and perverse generation, among whom you shine as lights in the world, holding fast the word of life, so that in the day of Christ I may be proud.