What does Romans 11:16 mean?

Paul's statements in the previous verses assumed that Israel would one day be accepted by God again as the Jewish people turned to faith in Christ. Israel, as a nation, would regain her special relationship with God. Paul now seems to say this destiny is in Israel's very nature. It is Israel's identity to be the people of God despite this temporary state of estrangement because of Israel's rejection of Christ as the Messiah.

Paul offers two illustrations to make this point. First, a bit of dough mixed into a larger lump of dough can determine what the entire mixture will be like. Paul is referencing Israel's practice of offering the first dough made from each year's harvest as a loaf of bread to the Lord (Numbers 15:20–21). That bit of dough offered as the "firstfruits" to the Lord was set apart. It was holy. Its holiness conferred holiness onto everything else made with that lump of dough.

The second illustration is one Paul will build on in the following verses. The nature of branches is determined by the "root" from which they grow. The basic Greek word used here is rhiza, referring to the core part of the plant, from the surface and reaching below the soil. If this root is holy, Paul implies, the branches will be holy as well.

Paul's larger point seems to be that Israel's firstfruits were the patriarchs. God set those first Israelites apart as His people. He made them holy in a sense. In that same sense, Paul says, their holiness will determine the ultimate nature of Israel. That's why she must eventually return to a right relationship with God, which now comes through faith in Christ.

Alternatively, some interpreters suggest that the firstfruits Paul has in mind are not the patriarchs, but the first Jewish people to trust in Christ. Their place in Christ will eventually lead to strengthen Israel's faith in Christ, as well.