How do we know that grace does not run in families?

The assertion that grace does not run in families is supported by Romans 9:6-8, where Paul acknowledges that not all of Abraham’s descendants are considered children of God. Paul asserts that physical descent alone does not confer spiritual status; rather, it is those who are children of the promise who are counted as God's people. This is illustrated in the examples of Isaac and Jacob, who were chosen by God despite their familial ties. Thus, familial relationships do not guarantee salvation, reinforcing the biblical truth that grace is bestowed upon individuals by God's sovereign choice, independent of their parental lineage.