This was in line with the Polish policy of being the Rzczpospolita (Republic) of 4 nations: Poles, Lithuanians, Ruthenians (ancestors of modern day Belarussians and Ukrainians) and Jews. The republic had freedom of religion for Catholics, Orthodox, Jews, Lutherans (Ewangelico Augusburgo), Reformed, Unitarians and Jews.
This freedom slowly changed after the 1600s "Swedish deluge" when Protestant Sweden swamped and destroyed the country aided to some extent by Orthodox Russia.
This caused a tightening of religion and nationalism, but this was both Jews and Catholics tied together as Poles. That union remained through the partitions of Poland (1793..) and the 127 years as a non-existent nation.
It only showed signs of fracture in the 1920s when Soviet forces pushed forward (read the Miracle on the Vistula for how Poland held back the Soviets from crossing into Western Europe) and the politics of Dmowski tried to show that the leaders of communism (Marx etc. ) were Jews -- the irony is that on the communist side too, the Jews were portrayed as emblems of capitalism (the Rothschilds)
Poland has the largest number of people in the Yad Vesham (hall of righteous Gentiles in Israel) even though in Poland if any family safeguarded a Jew, the entire family was to be shot by the Nazis.
Even today there is a sense of a wound -- you can't have 40% of your population (Jews were 20% of the population and half of the victims of the nazis -- the Poles were the other big chunk and the Gypsies were slaughtered with even more cruelty) disappear without a sense of "what happened"
In 1968, there were still 40,000 Jews in Poland, but there was an “anti-Zionist” purge implemented by Gomulka, that forced most of the remaining Jews to leave Poland.