It might be difficult to understand how God can have a 'special' people and yet judge them severely.  Well, God chose the line of Abraham to Isaac to Jacob (he was later renamed ‘Israel’) - from whom the 'children of Israel' were descended.  God entered into a covenant with them including the giving of the law.  So, they had a great privilege, but it was their responsibility to keep the covenant (Genesis 17:9-10).

Alas, all of them broke God's covenant.  But God graciously prescribed sacrifices - through which they admitted their sin, appealed for God’s mercy and appeased His wrath.  However, although God gave them many opportunities, they still failed Him and eventually judgement came in the form of invading armies who carried them off into exile. But God kept faith alive in a few hearts (including Isaiah's) and a remnant was preserved: a continuation of a thin line of faith up to the birth of Jesus.  They were the people who trusted the character of God and relied on His mercy.

So, there was no reason for the Jewish Christians in Rome to be smug about their heritage.   Most of their kin had squandered their special privilege.  There was no 'special entry' into the church for Jews.  Both Jews and Gentiles came on exactly the same terms - by faith in the grace of God and the sin-sacrifice of Jesus Christ (the new covenant). It is still the only way to find peace with God (www.crosscheck.org.uk).

Although the Jewish community in Rome had felt that their security was based on being a descendent of Abraham, Paul was helping them to see that his line of faith led to Jesus (John 8:56).  It is only by trusting in Jesus that both Jews and Gentiles can find eternal security in God.  Without that faith in Jesus as Saviour and Lord, people (however religious they might be) are still in as much danger as Sodom and Gomorrah, whose destruction matched the lack of righteousness that comes through faith (Genesis 18:20-32).  The Lord Almighty now has His descendants, His children who trust in Jesus, you and me: we have the responsibility to live righteously because of our faith and “… snatch others from the fire.” (Jude 1:23)