The Hebrew word translated there as "purpose" is ma’aneh (#04617 מַעֲנֶה) and it means "answer, or response".
Strong's Hebrew: 4617. מַעֲנֶה (maaneh) -- an answer, response
God has an answer for every behavior, including a response for those who choose to do evil.
God does not predetermine which people will be good and which people will be evil. Likewise He does not determine whom He will save. God wants the wicked to turn from their evil ways so they might live (Eze 33:11). But if they don't, there's a day of judgment coming, and God will have an answer for how the wicked chose to behave.