When Tārā assumes the characteristics of Śiva, Kālī will become the counterpart - Śakti and when Kālī assumes the job of Śiva, Tārā becomes Śakti. The sensible sādhaka therefore, should never understand any difference between them and so receives liberated, by worshipping equally and turns into 1 with Śiva https://www.youtube.com/watch?v=GMMWwN9ho2U&t=6s