For just as you were at one time disobedient to God but now have received mercy because of their disobedience,  so they too have now been disobedient in order that by the mercy shown to you they also may now receive mercy. (ESV)
I can remember my father correcting me as a child if I was pointing my finger at someone else. He was quick to remind me that every time I point the finger at someone there are four fingers pointing back at me. We love to point the finger. It is far easier to point out someone else's sin than it is to honestly deal with our own.
There is no question that the Jewish people had rebelled against their God. They had killed the Messiah that was promised to them. The Apostle Peter said it this way: "This Jesus, delivered up according to the definite plan and foreknowledge of God, you crucified and killed by the hands of lawless men. (Acts 2:23, ESV)"
The Gentiles were aware of the sins of the Israelites. It would have been very easy for them to point their fingers at the Jews. The Apostle Paul reminds the Gentiles, and all of us today, that the Jews were disobedient; and so were we. The Jews were disobedient and God offered mercy to the Gentiles. The Gentiles have been disobedient and God shows mercy to the Israelites.
The point is simple here. God is the the author of mercy. Mankind is the one prone to disobedience. No one has any grounds to point the finger at the other. We are all guilty. Every single one of us from every race of people on Earth are dependent on the mercy of God to rescue us from our terrible condition of disobedience.
When you see someone who is walking in disobedience do not point the finger. You are both equally guilty. Rejoice in God's mercy. Pray for the other person that they also would experience God's mercy.