Paul has a problem. There’s a church in Rome that he hasn’t been able to visit yet due to more pressing matters (Rom 1:8–15; 15:22–29). He would like to teach them in person, but in the meantime he wants them to be “full of goodness, filled with all knowledge, and able to instruct one another” (15:14)—to find the right answers to big questions on their own, at least until he can get to them.

Trouble is, the Roman believers are mostly Gentiles (non-Jewish people) who are geographically and culturally distant from Jerusalem. They are ignorant of the rich cultural heritage of the Jewish faith, and susceptible to the same Jewish and Gentile integration problems that plagued the church in Galatia (see Gal 3). If these non-Jewish Christians are going to have any chance at getting things right on their own, they’re going to need a systematic introduction to Jewish history and their place in it.

Paul’s letter to the Romans is more than just a set of philosophical propositions about the nature of God or the work of Christ. It’s a crash course in biblical history for those wishing to transition from the worldly and fleshly culture of the “old man” (Rom 6:6) into their new role as God’s people (8:15, 23). Paul hits all the highlights of Israel’s history—from creation and the fall, to the Abrahamic covenant (Gen 12, 15, and 18; Rom 4), to the exodus (Exod 1–2; 14; Rom 5–6), to the giving of the Mosaic Law. He carefully relates each episode to the situation faced by Roman believers.

Paul’s focus is integrating Gentile believers into a tradition inaugurated by Jews (while not converting to Judaism in the process). In chapter 11, Paul uses a powerful metaphor to illustrate how Gentile believers are integrated into the body of Christ. They are “wild shoots” who are “grafted” onto the trunk of true faith (Rom 11:17–24). Jews who have rejected Christ are “natural branches” who have been “broken off” to make room.

Grafting branches from one tree onto the rootstock of another was common practice at the time:

The normal process was to take a shoot from an olive tree that bears good fruit though it does not grow vigorously and graft it onto a wild olive stock, whose fruit is poor but which grows strongly. The result is a tree with vigorous growth which bears good olives. Paul, however, talks of the reverse process, of grafting a wild olive onto the stock of a good olive and later even of grafting back some of the good olive branches that have been cut out.

The “root” of the Jewish faith sustains and nurtures Gentile “branches,” which would otherwise not bear good fruit. New believers should not disdain their Jewish forbearers, since “it is not you who support the root, but the root that supports you” (11:18). The Gentiles are inheriting Jewish customs, practices and (most importantly) promises—not the other way around.