Do you understand that Paul is teaching that the Jews who fell into unbelief, and were subsequently "broken off" from covenant relationship, in which the Gentiles who believed we "grafted in", as it were, to the natural olive tree.
- 20 Well said. Because of unbelief they were broken off, and you stand by faith. Do not be haughty, but fear.
In addition Paul warns the now believing Gentiles, that they could suffer the same fate, if they do not continue.
- 21 For if God did not spare the natural branches, He may not spare you either. 22 Therefore consider the goodness and severity of God: on those who fell, severity; but toward you, goodness, if you continue in His goodness. Otherwise you also will be cut off.
He also says these Jews who fell into unbelief, and are now enemies of the Gospel and were removed from covenant relationship, can indeed be grated back in, IF they do not continue in unbelief.
- 23 And they also, if they do not continue in unbelief, will be grafted in, for God is able to graft them in again.
28 Concerning the gospel they are enemies for your sake, but concerning the election they are beloved for the sake of the fathers. 29 For the gifts and the calling of God are irrevocable. Romans 11:28-29