What does it mean that believers are God's workmanship?
Being God's workmanship means believers are not saved by works but by grace through faith, and God then continues His work in them. They are the result of a divine re-creation, created for the next step of God's purpose, so no one can brag.
Les explains that salvation is by grace through faith, not of yourselves; it is the gift of God, not of works, so no one can boast. But verse 10 shows it does not stop there. Believers are not saved merely to go their own way and do nothing. God has the next step in their life as a believer: they are His workmanship, the result of a recreation of God Himself, now a workmanship created.