If a part is holy, the whole is holy (Romans 11:16)
In Haggai 2:11-14, God makes the point that holiness cannot be transferred to something else by association. For something to be holy, it must be intrinsically holy. However, this is not true for something that is profane or unclean. Uncleanness can be transferred by association.
Paul shows another application of the same concept. When the harvest is gathered, the first fruits are offered to God (Numbers 15:19-21). If portion that is used to give an offering to God is holy, then the whole from which it came must also be holy. After the offering is made to God, the harvest is then available to the people (Leviticus 23:14). In a sense, it becomes dedicated, or holy, for their use.
Using the illustration of a tree to represent God and His people, if the root (God) is holy, then the branches (the people) must also be holy (Leviticus 11:44-45; 20:7-8; I Peter 1:16).
The first converts to Christianity came from the Jews (Romans 1:16). If they could become holy and dedicated to God, then all the Jews could also be holy. They weren’t rejected just because they were Jews. If the part, then so must be the whole.
The Gentiles are not superior (Romans 11:17-18)
Continuing the illustration of a tree, if some of the Jews were removed and Gentiles took their place, it wasn’t because the Gentiles were a superior race of people. Rather they were less productive wild olive trees. There were some good people among the Gentiles (Romans 2:13-15). Cornelius is an example of such people (Acts 10:1-2). Sure, it was harder to be fruitful to God and a Gentile, but not impossible.
These Gentile branches were grafted in and so they were not superior to the Jewish branches that were already there. It is the tree to which they are connected that makes them holy, and not the other way around (John 15:4).
God treats all people equally (Romans 11:19-22)
It might appear that many of the Jews were removed in order to make room for the Gentiles. However, the Jews who were removed had been removed because of their unbelief (Hebrews 3:18-19). The Gentiles who had been grafted in were grafted in because of their belief. That simple fact should make the Gentiles tremble because their place in the tree (God’s kingdom) is not guaranteed to be permanent (Proverbs 28:14). It depends on their continued faith, otherwise they, too, will be removed like the Jews.
The Jews can be restored (Romans 11:23-24)
If Jews stop their unbelief, God will graph them back into the tree. Just as a place in the tree is not guaranteed to be permanent, the exclusion is not permanent either. It depends on the individual’s faith (II Corinthians 3:16). If God was able to graft in Gentiles who were by nature not followers of God and cause them to become productive people, then surely it would be even easier for God to restore the Jews back to their original place to become productive people once again.