When Tārā assumes the traits of Śiva, Kālī results in being the counterpart - Śakti and when Kālī assumes the function of Śiva, Tārā will become Śakti. The smart sādhaka thus, ought to never perceive any distinction between them and thus receives liberated, by worshipping both of those and https://www.youtube.com/watch?v=GMMWwN9ho2U&t=6s