The Plan of Salvation is not just the plan of the Father, it is also the plan of our Heavenly Mother.
Many Church leaders, from Joseph Smith to Russel M. Nelson, have taught of Heavenly Mother.
The teaching that we have a Heavenly Mother is a core doctrine. Some other teachings about Her are supporting doctrine.
Because knowledge of Heavenly Mother is essential to our understanding of the Plan of Salvation and our divine potential, knowledge of Her is essential to our salvation and exaltation.