Whether we are religious (circumcised Jews) or not (uncircumcised Gentiles), there is one God, and one way to be right with him—through faith (v.29–30). To stop boasting is to realize that our best achievements have done nothing to justify us, and that our worst failings do not exclude us.
On what principle is boasting excluded? (v.27)
"Dear Lord, thank you that through Christ’s sacrifice for me, I am your child. Thank you that I can face the day knowing I lack nothing in this world, and the world can take nothing from me. I have Christ. I thank you and praise you. Amen."
How does faith in Christ “uphold” the law? First, because it shows the law must be kept in order for someone to be righteous—in Christ’s life, it was. Second, it shows that law-breaking will be punished—in Christ’s death, it was. Third, it enables us to love the beauty of the law rather than hating it. If we are obeying to be saved, we will either change the law to make keeping it easier, or be crushed by the law because keeping it is impossible. Only the gospel allows us to care about justice and know we are forgiven.
What does faith in Christ actually help us to do? (v.31)
"Dear Lord, help me not to take your law lightly. Thank you for the gift of faith that allows me to trust in your righteousness and the gift of your Spirit that I don’t have to go it alone! Help me to see the beauty and the blessing in keeping your commands and walking by the Spirit. In Jesus’ name I pray, Amen."
To be one “who does not work” does not mean a saved person does not obey the law, but that they no longer trust in obeying the law (“work”) to be saved. They transfer their trust from themselves and their efforts to God and his promises.