What Does The Ending Of mother! Really Mean?

6. Octagons, Christ And The Idea Of Infinity

The shape of the house is very important in mother! as it suggests that this loop of creation and destruction is perpetual and had trapped Him and his various mother figures forever.

Symbolically, octagons in architecture are said to represent infinity (as well as offering pleasant aesthetic benefits) as Aronofsky discovered in his research for the film:

“There are all of these alchemy theories about the octagon and numeric beliefs about the number eight and about infinity and regeneration. The reason I like the octagon shape as a filmmaker was when I shot through a doorway you’re not looking at a flat wall. You’re looking at a diagonal wall that adds depth and just makes things more interesting.”

The director also discovered that Victorian scientists believed that the octagon was the perfect shape for the brain, which in turn influenced the way some houses of the period were designed. And specifically, when an octagon is fused in design with a dome (as in the case of the film's house's roof) it symbolises the fusing of the spiritual with the physical.

In short, the links to spiritual considerations and the ship are impossible to ignore, which is why there are so many in the film, and it's perhaps best to consider Freddy Silva's analysis of the shape from Legacy Of The Gods:

(The octagon) "represents the ultimate balance between material and invisible forces, the fixed male and mutable female; total balance between material and spiritual, heart and mind: the fully aware, 'christed' human. It is both the inhalation and the exhalation of the breath of creation... the octagon symbolizes the ultimate aim of esoteric traditions. Notable, enlightened figures throughout history such as Mohammed, Merlin, the archangel Michael and Jesus have been characterized by either the octagon or its numerical value 8, and the infinity symbol; in gematria the name Jesus carries the value of 888."