Well to start Polish kings invited Jews to settle in the region, and gave them rights. A combination of devastation from the Mongol invasions and the expulsion of the Jews from the West during the Crusades led to large numbers of Jews coming to Poland around the 1200s. They were guaranteed protection by a charter issued by Duke Boleslaw in 1264, which was actually loosely based on a similar proclamation Austria made in 1244. In short it gave the Jews the freedom to practise their religion and settle in the cities, in effect not making any distinction between them and Christians.

Why the Polish kings wanted the Jews is simple enough: after the Mongols the land had been devastated, and they needed both people and capital to keep the kingdom going. Jews were able to supply both of those, and served as lead bankers for the Polish government for centuries. They also gradually took on a role as landlord for the nobility, managing vast properties in the name of Christian rulers. This however bred resentment by the peasants, who saw the Jews as exploiters, which ultimately had the effect of turning the population against them, much like Western Europe. Cities that gained charters moved to expel their Jews, and thus ghettos were established around them (Kazimierz in Krakow is probably the most famous). This resentment was a factor in the Khmelnitsky uprising in 1648, which saw upwards of 20,000 Jews killed.

So while most of Europe didn't want Jews because they lent money and were heavily involved in skilled trades, Poland wanted them precisely because of that. That only changed when the population began to felt threatened by the growing influence of the Jews, a process that took centuries to fully occur and see results.