If your faith is rooted in the gospel of Zion, in the good news of Jesus’s life, death, and resurrection on your behalf, you are already a member of the “heavenly Jerusalem”
When we believe in Jesus as the true and better fulfillment of every promise made to Abraham, we, too, are counted as righteous in the same way that he was — by faith.
Paul has zero patience for the gospel of God to be called into question, especially when the ones questioning it are the ones who should’ve known better.
All of Scripture, every last syllable of it, is meant to drive us to "consider Jesus," the One who comes to "make us right" by gifting us his righteousness.