Paul is speaking of a situation that did not exist to emphasize that the inheritance came only by means of the promise. Alternate translation: "The inheritance comes to us by means of the promise because we could not keep the demands of God's law" (See: [[rc://en/ta/man/translate/figs-hypo]])
What God has promised believers is spoken of as if it were an inheritance of property and wealth from a family member, and eternal blessings and redemption. (See: [[rc://en/ta/man/translate/figs-metaphor]])