St. Peter referred to those Jewish people who refused to convert to Christianity as the Faithless People. He did this because the Jewish faith was the result of a covenant begun by God in Abraham. This covenant was a promise of things that God would fulfill for Abraham and his descendants if Abraham and his descendants would become his faithful choosen people.
This covenant was passed down through the generations until it reached Moses who received from God additions to his covenant. One of these conditions was the law and the other the direction that all the faithful must keep the law and await the coming of the Messiah. It was always understood that the Messiah would be the rightful authority over all God’s people. The King of God’s chosen people.
Jesus came and in him was fulfilled, at least to God’s satisfaction, all the remaining promises that had been made to Abraham. Many of the Jewish people of that time converted. We know from the bible that on one day 3000 and on another 5000 this does not remotely make us aware of the vast numbers that finally decided to follow the true Messiah over the next 1000 years. It may be that the majority of the Jewish people of that time did convert to Christianity over time.
Christianity is an entirely new covenant. It is not a continuation of the first but a fulfillment of the first and the creation of an entirely knew promise from God for his people. A promise or covenant that is fulfilled no longer exists except as history. Because the original promise to Abraham was fulfilled in Christ, and a new promise made, St. Peter could only see his people, who refused to follow the true Messiah, as people living a faith no longer based on any promise from God, therefore without a true faith. Hence the term, “The Faithless People.”
Does the Church today like St. Peter actually believe that the Jewish people are practicing a religion based on a covenant that really doesn’t exist?