Why does Paul digress in Romans 9-11?

Paul digresses in Romans 9–11 because these three chapters are parenthetical. He turns aside to deal with the Jew: chapter 9 covers Israel’s past, chapter 10 God’s present dealing with Israel, and chapter 11 Israel’s future. Afterward, the text returns to the flow of Romans 8 and proceeds to chapter 12.

Les explains that Romans 9, 10, and 11 are parenthetical chapters sitting in the middle of the book of Romans. Paul suddenly digresses to deal with the Jew. Chapter 9 addresses Israel’s past, chapter 10 addresses God’s dealing with Israel in the present, and chapter 11 addresses Israel’s future. Then the book returns to where it left off with Romans 8 and moves into chapter 12.

Romans 9

Romans 10

Romans 11

Why does Paul go back to the Old Testament in Romans 9?

Paul returns to the Old Testament in Romans 9 because the chapter deals with Israel's past and he must draw repeatedly on those Scriptures to make his point. This establishes God's continuing covenant relationship with Israel, showing He has not permanently set the nation aside despite the present age.