Historically, in christian beliefs, the intermediate state where an opportunity for purification is offered to eliminate any remaining obstacles to full enjoyment of eternal union with god is called

I believe the correct answer is: purgatory.

Historically, in Roman Christian theology, purgatory represent the beliefs of intermediate state after physical death where an opportunity for purification is offered to eliminate any remaining obstacles to achieve the holiness necessary to enter the joy of heaven and full enjoyment of eternal union with God.