Egkentrizo is an agricultural term meaning to graft a shoot into a tree — to insert a branch from one plant into the stock of another so it becomes part of the living whole. It appears only in Romans 11:17-24, where Paul uses olive grafting as a metaphor for Gentile inclusion in God's covenant people.
Paul's grafting metaphor in Romans 11 is one of the most important passages on Jewish-Gentile relations in the New Testament. Natural branches (Jewish people who rejected Christ) were broken off from the olive tree; wild branches (Gentiles) were egkentrizo — grafted in, contrary to nature. This is entirely an act of grace, not Gentile merit. Paul's warning is sobering: if God did not spare the natural branches for unbelief, He will not spare the grafted branches for arrogance. And hope remains: the natural branches can be re-grafted if they believe (Romans 11:23-24). The olive tree is Israel's covenant, and all who are in Christ — Jew or Gentile — are part of the one tree.