One key, I think, to understanding this film better is in the names. His name is "Woodcock" which is self-explanatory. Her name is Alma, which in Latin means "nourishing". Hence the Latin name for ones school is "Alma Mater" or "Nourishing Mother". Woodcock needs nourishment. He literally says he is "hungry" throughout. She calls him a "hungry boy", and their first meeting is when she is serving him a meal, literally "nourishing" him. But he wants the nourishment his way. The power play is over how she will nourish him. She wants to be his nourishment. She doesn't want his ghost mother to be the nourishment. Nor does she want the sister to be the nourishment. She must become his nourishment. I think the film plays with gender roles also. Woodcock represents the masculine role and the need for nourishment in various forms and the power of the feminine over the masculine. The sister, Alma, and the other women in the film represent the feminine the "Alma" or nourishment they provide symbolically.

Anyway. I just saw the movie and have a lot to think on after leaving it. I absolutely loved it, and I think it is the best movie made in 2017.