" The religious controversies of the late 16th and early 17th century highlighted several pregnant issues in Ukrainian society. They placed the growing tensions with the Catholic Poles on an ideological and highly emotional level. Indeed, Catholic Poland now emerged as the antithesis of Ukrainian society. But the cultural confrontation between the Ukrainians and the Poles cost the former dearly: it forced Ukrainian nobles to choose between their own stagnant, impoverished cultural heritage and the vibrant, attractive Catholic /Polish culture. Not suprisingly, the vast majority opted for Catholicism and the Polonization that invariably followed.
Consequently, the Ukrainians lost their noble elite. And this development was of epochal importance for their sub sequent history.

Another far-reaching by-product of the Orthodox /Catholic confrontation, specifically of the Union of Brest, was that it divided Ukrainians into Orthodox and Greek Catholics, thereby laying the foundation for the many sharp distinctions that eventually developed between East and West Ukrainians. But the period was not merely one of setbacks for Ukrainian society: the religious controversies sparked a cultural upsurge within it and the confrontation with the Poles led to a sharper definition of a Ukrainian identity. "

― Orest Subtelny , Ukraine: A History